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74-559: Typically, buffer overflow protection modifies the organization of stack-allocated data so it includes a canary value that, when destroyed by a stack buffer overflow, shows that a buffer preceding it in memory has been overflowed. By verifying the canary value, execution of the affected program can be terminated, preventing it from misbehaving or from allowing an attacker to take control over it. Other buffer overflow protection techniques include bounds checking , which checks accesses to each allocated block of memory so they cannot go beyond

148-413: A canary in a coal mine , are used to detect a stack buffer overflow before execution of malicious code can occur. This method works by placing a small integer, the value of which is randomly chosen at program start, in memory just before the stack return pointer. Most buffer overflows overwrite memory from lower to higher memory addresses, so in order to overwrite the return pointer (and thus take control of

222-412: A buffer and control data on the stack to monitor buffer overflows. When the buffer overflows, the first data to be corrupted will usually be the canary, and a failed verification of the canary data will therefore alert of an overflow, which can then be handled, for example, by invalidating the corrupted data. A canary value should not be confused with a sentinel value . The terminology is a reference to

296-427: A computer. Typically, buffer overflow protection modifies the organization of data in the stack frame of a function call to include a "canary" value that, when destroyed, shows that a buffer preceding it in memory has been overflowed. This provides the benefit of preventing an entire class of attacks. According to some researchers, the performance impact of these techniques is negligible. Stack-smashing protection

370-446: A fixed length for machine opcodes, this machine limitation can make the technique of jumping to the stack almost impossible to implement (with the one exception being when the program actually contains the unlikely code to explicitly jump to the stack register). Within the topic of stack buffer overflows, an often-discussed-but-rarely-seen architecture is one in which the stack grows in the opposite direction. This change in architecture

444-464: A local stack variable c . This works fine for command-line arguments smaller than 12 characters (as can be seen in figure B below). Any arguments larger than 11 characters long will result in corruption of the stack. (The maximum number of characters that is safe is one less than the size of the buffer here because in the C programming language, strings are terminated by a null byte character. A twelve-character input thus requires thirteen bytes to store,

518-407: A non-protected region of memory. This method is becoming more popular now that hardware support for the no-execute flag is available in most desktop processors. While this method prevents the canonical stack smashing exploit, stack overflows can be exploited in other ways. First, it is common to find ways to store shellcode in unprotected memory regions like the heap, and so very little need change in

592-502: A null character, while the undesirable result is that the canary is known. Even with the protection, an attacker could potentially overwrite the canary with its known value and control information with mismatched values, thus passing the canary check code, which is executed soon before the specific processor's return-from-call instruction. Random canaries are randomly generated, usually from an entropy -gathering daemon , in order to prevent an attacker from knowing their value. Usually, it

666-472: A random bit XORed with a non-random bit will result in a random bit. Multiple sources of potentially random data can be combined using XOR, and the unpredictability of the output is guaranteed to be at least as good as the best individual source. XOR is used in RAID 3–6 for creating parity information. For example, RAID can "back up" bytes 10011100 2 and 01101100 2 from two (or more) hard drives by XORing

740-451: A segmentation fault, terminating the program. It may still be possible to read the canary if the attacker knows where it is or can get the program to read from the stack. Random XOR canaries are random canaries that are XOR-scrambled using all or part of the control data. In this way, once the canary or the control data is clobbered, the canary value is wrong. Random XOR canaries have the same vulnerabilities as random canaries, except that

814-486: A simple adder can be made with an XOR gate to add the numbers, and a series of AND, OR and NOT gates to create the carry output. On some computer architectures, it is more efficient to store a zero in a register by XOR-ing the register with itself (bits XOR-ed with themselves are always zero) than to load and store the value zero. In cryptography , XOR is sometimes used as a simple, self-inverse mixing function, such as in one-time pad or Feistel network systems. XOR

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888-557: Is a group . This unfortunately prevents the combination of these two systems into larger structures, such as a mathematical ring . However, the system using exclusive or ( { T , F } , ⊕ ) {\displaystyle (\{T,F\},\oplus )} is an abelian group . The combination of operators ∧ {\displaystyle \wedge } and ⊕ {\displaystyle \oplus } over elements { T , F } {\displaystyle \{T,F\}} produce

962-408: Is a compiler-based technique that adds run-time bounds information for each allocated block of memory, and checks all pointers against those at run-time. For C and C++, bounds checking can be performed at pointer calculation time or at dereference time. Implementations of this approach use either a central repository, which describes each allocated block of memory, or fat pointers , which contain both

1036-400: Is a type of the more general programming malfunction known as buffer overflow (or buffer overrun). Overfilling a buffer on the stack is more likely to derail program execution than overfilling a buffer on the heap because the stack contains the return addresses for all active function calls. A stack buffer overflow can be caused deliberately as part of an attack known as stack smashing . If

1110-557: Is also found in other languages. However, many languages have disjunctive constructions which are robustly exclusive such as French soit... soit . The symbol used for exclusive disjunction varies from one field of application to the next, and even depends on the properties being emphasized in a given context of discussion. In addition to the abbreviation "XOR", any of the following symbols may also be seen: If using binary values for true (1) and false (0), then exclusive or works exactly like addition modulo 2. Exclusive disjunction

1184-497: Is also heavily used in block ciphers such as AES (Rijndael) or Serpent and in block cipher implementation (CBC, CFB, OFB or CTR). In simple threshold-activated artificial neural networks , modeling the XOR function requires a second layer because XOR is not a linearly separable function. Similarly, XOR can be used in generating entropy pools for hardware random number generators . The XOR operation preserves randomness, meaning that

1258-478: Is called the function's algebraic normal form . Disjunction is often understood exclusively in natural languages . In English, the disjunctive word "or" is often understood exclusively, particularly when used with the particle "either". The English example below would normally be understood in conversation as implying that Mary is not both a singer and a poet. However, disjunction can also be understood inclusively, even in combination with "either". For instance,

1332-414: Is combined with a non-executable stack the attacker can use this fixed region of memory. Therefore, all programs should be compiled with PIE (position-independent executables) such that even this region of memory is randomized. The entropy of the randomization is different from implementation to implementation and a low enough entropy can in itself be a problem in terms of brute forcing the memory space that

1406-637: Is compiled with -fstack-protector since 2011. All Arch Linux packages built since 4 May 2014 use -fstack-protector-strong . Stack protection is only used for some packages in Debian , and only for the FreeBSD base system since 8.0. Stack protection is standard in certain operating systems, including OpenBSD , Hardened Gentoo and DragonFly BSD . StackGuard and ProPolice cannot protect against overflows in automatically allocated structures that overflow into function pointers. ProPolice at least will rearrange

1480-550: Is equivalent to the disjunction of the negation of its antecedent and its consequence) and material equivalence . In summary, we have, in mathematical and in engineering notation: By applying the spirit of De Morgan's laws , we get: ¬ ( p ↮ q ) ⇔ ¬ p ↮ q ⇔ p ↮ ¬ q . {\displaystyle \lnot (p\nleftrightarrow q)\Leftrightarrow \lnot p\nleftrightarrow q\Leftrightarrow p\nleftrightarrow \lnot q.} Although

1554-451: Is frequently suggested as a solution to the stack buffer overflow problem because any overflow of a stack buffer that occurs within the same stack frame cannot overwrite the return pointer. However, any overflow that occurs in a buffer from a previous stack frame will still overwrite a return pointer and allow for malicious exploitation of the bug. For instance, in the example above, the return pointer for foo will not be overwritten because

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1628-484: Is negligible, less than one percent. The resulting gdb issues were resolved by Mark Kettenis two years later, allowing enabling of the feature. Following this event, the StackGhost code was integrated (and optimized) into OpenBSD /SPARC. Stack canary In software, a stack buffer overflow or stack buffer overrun occurs when a program writes to a memory address on the program's call stack outside of

1702-445: Is not logically possible or plausible to read the canary for exploiting; the canary is a secure value known only by those who need to know it—the buffer overflow protection code in this case. Normally, a random canary is generated at program initialization, and stored in a global variable. This variable is usually padded by unmapped pages so that attempting to read it using any kinds of tricks that exploit bugs to read off RAM cause

1776-469: Is often used for bitwise operations. Examples: As noted above, since exclusive disjunction is identical to addition modulo 2, the bitwise exclusive disjunction of two n -bit strings is identical to the standard vector of addition in the vector space ( Z / 2 Z ) n {\displaystyle (\mathbb {Z} /2\mathbb {Z} )^{n}} . In computer science, exclusive disjunction has several uses: In logical circuits,

1850-427: Is provided (with an executable stack) or one is constructed using code reuse such as in ret2libc or return-oriented programming (ROP). Randomizing the memory layout will, as a concept, prevent the attacker from knowing where any code is. However, implementations typically will not randomize everything; usually the executable itself is loaded at a fixed address and hence even when ASLR (address space layout randomization)

1924-422: Is randomized. The previous mitigations make the steps of the exploitation harder. But it is still possible to exploit a stack buffer overflow if some vulnerabilities are presents or if some conditions are met. An attacker is able to exploit the format string vulnerability for revealing the memory locations in the vulnerable program. When Data Execution Prevention is enabled to forbid any execute access to

1998-398: Is sometimes useful to write p ↮ q {\displaystyle p\nleftrightarrow q} in the following way: or: This equivalence can be established by applying De Morgan's laws twice to the fourth line of the above proof. The exclusive or is also equivalent to the negation of a logical biconditional , by the rules of material implication (a material conditional

2072-413: Is standard in certain operating systems, including OpenBSD . Intel's C and C++ compiler supports stack-smashing protection with options similar to those provided by GCC and Microsoft Visual Studio. Fail-Safe C is an open-source memory-safe ANSI C compiler that performs bounds checking based on fat pointers and object-oriented memory access. Invented by Mike Frantzen , StackGhost is a simple tweak to

2146-559: Is unable to protect against certain forms of attack. For example, it cannot protect against buffer overflows in the heap. There is no sane way to alter the layout of data within a structure ; structures are expected to be the same between modules, especially with shared libraries. Any data in a structure after a buffer is impossible to protect with canaries; thus, programmers must be very careful about how they organize their variables and use their structures. Canaries or canary words or stack cookies are known values that are placed between

2220-657: The -fstack-protector-strong flag to strike a better balance between security and performance. This flag protects more kinds of vulnerable functions than -fstack-protector does, but not every function, providing better performance than -fstack-protector-all . It is available in GCC since its version 4.9. All Fedora packages are compiled with -fstack-protector since Fedora Core 5, and -fstack-protector-strong since Fedora 20. Most packages in Ubuntu are compiled with -fstack-protector since 6.10. Every Arch Linux package

2294-561: The GNU Compiler Collection , LLVM , Microsoft Visual Studio , and other compilers. A stack buffer overflow occurs when a program writes to a memory address on the program's call stack outside of the intended data structure, which is usually a fixed-length buffer. Stack buffer overflow bugs are caused when a program writes more data to a buffer located on the stack than what is actually allocated for that buffer. This almost always results in corruption of adjacent data on

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2368-520: The Immunix Linux distribution from 1998 to 2003, and was extended with implementations for terminator, random and random XOR canaries. StackGuard was suggested for inclusion in GCC 3.x at the GCC 2003 Summit Proceedings, but this was never achieved. From 2001 to 2005, IBM developed GCC patches for stack-smashing protection, known as ProPolice . It improved on the idea of StackGuard by placing buffers after local pointers and function arguments in

2442-641: The SUID bit set to run as the superuser ), then the attacker could use this vulnerability to gain superuser privileges on the affected machine. The attacker can also modify internal variable values to exploit some bugs. With this example: There are typically two methods that are used to alter the stored address in the stack - direct and indirect. Attackers started developing indirect attacks, which have fewer dependencies, in order to bypass protection measures that were made to reduce direct attacks. A number of platforms have subtle differences in their implementation of

2516-779: The infix operators XOR ( / ˌ ɛ k s ˈ ɔː r / , / ˌ ɛ k s ˈ ɔː / , / ˈ k s ɔː r / or / ˈ k s ɔː / ), EOR , EXOR , ∨ ˙ {\displaystyle {\dot {\vee }}} , ∨ ¯ {\displaystyle {\overline {\vee }}} , ∨ _ {\displaystyle {\underline {\vee }}} , ⩛ , ⊕ {\displaystyle \oplus } , ↮ {\displaystyle \nleftrightarrow } , and ≢ {\displaystyle \not \equiv } . The truth table of A ⊕ B {\displaystyle A\oplus B} shows that it outputs true whenever

2590-423: The logical conjunction ("logical and", ∧ {\displaystyle \wedge } ), the disjunction ("logical or", ∨ {\displaystyle \lor } ), and the negation ( ¬ {\displaystyle \lnot } ) as follows: The exclusive disjunction p ↮ q {\displaystyle p\nleftrightarrow q} can also be expressed in

2664-516: The operating system , tagging can also be used to detect buffer overflows. An example is the NX bit hardware feature, supported by Intel , AMD and ARM processors. Stack-smashing protection was first implemented by StackGuard in 1997, and published at the 1998 USENIX Security Symposium . StackGuard was introduced as a set of patches to the Intel x86 backend of GCC 2.7. StackGuard was maintained for

2738-529: The operators ∧ {\displaystyle \wedge } ( conjunction ) and ∨ {\displaystyle \lor } ( disjunction ) are very useful in logic systems, they fail a more generalizable structure in the following way: The systems ( { T , F } , ∧ ) {\displaystyle (\{T,F\},\wedge )} and ( { T , F } , ∨ ) {\displaystyle (\{T,F\},\lor )} are monoids , but neither

2812-434: The "read from stack" method of getting the canary is a bit more complicated. The attacker must get the canary, the algorithm, and the control data in order to re-generate the original canary needed to spoof the protection. In addition, random XOR canaries can protect against a certain type of attack involving overflowing a buffer in a structure into a pointer to change the pointer to point at a piece of control data. Because of

2886-494: The XOR encoding, the canary will be wrong if the control data or return value is changed. Because of the pointer, the control data or return value can be changed without overflowing over the canary. Although these canaries protect the control data from being altered by clobbered pointers, they do not protect any other data or the pointers themselves. Function pointers especially are a problem here, as they can be overflowed into and can execute shellcode when called. Bounds checking

2960-536: The above have motivated analyses of the exclusivity inference as pragmatic conversational implicatures calculated on the basis of an inclusive semantics . Implicatures are typically cancellable and do not arise in downward entailing contexts if their calculation depends on the Maxim of Quantity . However, some researchers have treated exclusivity as a bona fide semantic entailment and proposed nonclassical logics which would validate it. This behavior of English "or"

3034-522: The actually allocated space, and tagging , which ensures that memory allocated for storing data cannot contain executable code. Overfilling a buffer allocated on the stack is more likely to influence program execution than overfilling a buffer on the heap because the stack contains the return addresses for all active function calls. However, similar implementation-specific protections also exist against heap-based overflows. There are several implementations of buffer overflow protection, including those for

Buffer overflow protection - Misplaced Pages Continue

3108-401: The affected program is running with special privileges, or accepts data from untrusted network hosts (e.g. a webserver ) then the bug is a potential security vulnerability . If the stack buffer is filled with data supplied from an untrusted user then that user can corrupt the stack in such a way as to inject executable code into the running program and take control of the process. This is one of

3182-403: The affected program is running with special privileges, or if it accepts data from untrusted network hosts (for example, a public webserver ), then the bug is a potential security vulnerability that allows an attacker to inject executable code into the running program and take control of the process. This is one of the oldest and more reliable methods for attackers to gain unauthorized access to

3256-519: The allocation order to get such structures allocated before function pointers. A separate mechanism for pointer protection was proposed in PointGuard and is available on Microsoft Windows. The compiler suite from Microsoft implements buffer overflow protection since version 2003 through the /GS command-line switch, which is enabled by default since version 2005. Using /GS- disables the protection. Stack-smashing protection can be turned on by

3330-454: The attacker's ends. It is even possible to use "returnless" return-oriented programming by exploiting instructions or groups of instructions that behave much like a return instruction. Instead of separating the code from the data, another mitigation technique is to introduce randomization to the memory space of the executing program. Since the attacker needs to determine where executable code that can be used resides, either an executable payload

3404-497: The call stack that can affect the way a stack buffer overflow exploit will work. Some machine architectures store the top-level return address of the call stack in a register. This means that any overwritten return address will not be used until a later unwinding of the call stack. Another example of a machine-specific detail that can affect the choice of exploitation techniques is the fact that most RISC -style machine architectures will not allow unaligned access to memory. Combined with

3478-528: The compiler flag -qstackprotect . Clang supports the same -fstack-protector options as GCC and a stronger "safe stack" ( -fsanitize=safe-stack ) system with similarly low performance impact. Clang also has three buffer overflow detectors, namely AddressSanitizer ( -fsanitize=address ), UBSan ( -fsanitize=bounds ), and the unofficial SafeCode (last updated for LLVM 3.0). These systems have different tradeoffs in terms of performance penalty, memory overhead, and classes of detected bugs. Stack protection

3552-490: The execution never actually vectors to the stack itself. A variant of return-to-libc is return-oriented programming (ROP), which sets up a series of return addresses, each of which executes a small sequence of cherry-picked machine instructions within the existing program code or system libraries, sequence which ends with a return. These so-called gadgets each accomplish some simple register manipulation or similar execution before returning, and stringing them together achieves

3626-406: The first example below shows that "either" can be felicitously used in combination with an outright statement that both disjuncts are true. The second example shows that the exclusive inference vanishes away under downward entailing contexts. If disjunction were understood as exclusive in this example, it would leave open the possibility that some people ate both rice and beans. Examples such as

3700-399: The following way: This representation of XOR may be found useful when constructing a circuit or network, because it has only one ¬ {\displaystyle \lnot } operation and small number of ∧ {\displaystyle \land } and ∨ {\displaystyle \lor } operations. A proof of this identity is given below: It

3774-532: The historic practice of using canaries in coal mines , since they would be affected by toxic gases earlier than the miners, thus providing a biological warning system. Canaries are alternately known as stack cookies , which is meant to evoke the image of a "broken cookie" when the value is corrupted. There are three types of canaries in use: terminator , random , and random XOR . Current versions of StackGuard support all three, while ProPolice supports terminator and random canaries. Terminator canaries use

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3848-432: The input followed by the sentinel zero byte. The zero byte then ends up overwriting a memory location that's one byte beyond the end of the buffer.) The program stack in foo() with various inputs: In figure C above, when an argument larger than 11 bytes is supplied on the command line foo() overwrites local stack data, the saved frame pointer, and most importantly, the return address. When foo() returns, it pops

3922-596: The inputs differ: Exclusive disjunction essentially means 'either one, but not both nor none'. In other words, the statement is true if and only if one is true and the other is false. For example, if two horses are racing, then one of the two will win the race, but not both of them. The exclusive disjunction p ↮ q {\displaystyle p\nleftrightarrow q} , also denoted by p ? ⁡ q {\displaystyle p\operatorname {?} q} or J p q {\displaystyle Jpq} , can be expressed in terms of

3996-438: The intended data structure, which is usually a fixed-length buffer . Stack buffer overflow bugs are caused when a program writes more data to a buffer located on the stack than what is actually allocated for that buffer. This almost always results in corruption of adjacent data on the stack, and in cases where the overflow was triggered by mistake, will often cause the program to crash or operate incorrectly. Stack buffer overflow

4070-406: The just mentioned bytes, resulting in ( 11110000 2 ) and writing it to another drive. Under this method, if any one of the three hard drives are lost, the lost byte can be re-created by XORing bytes from the remaining drives. For instance, if the drive containing 01101100 2 is lost, 10011100 2 and 11110000 2 can be XORed to recover the lost byte. XOR is also used to detect an overflow in

4144-404: The logical "AND" operation as multiplication on F 2 {\displaystyle \mathbb {F} _{2}} and the "XOR" operation as addition on F 2 {\displaystyle \mathbb {F} _{2}} : The description of a Boolean function as a polynomial in F 2 {\displaystyle \mathbb {F} _{2}} , using this basis,

4218-400: The number of true inputs is odd . It gains the name "exclusive or" because the meaning of "or" is ambiguous when both operands are true. XOR excludes that case. Some informal ways of describing XOR are "one or the other but not both", "either one or the other", and "A or B, but not A and B". It is symbolized by the prefix operator J {\displaystyle J} and by

4292-430: The observation that most buffer overflow attacks are based on certain string operations which end at string terminators. The reaction to this observation is that the canaries are built of null terminators, CR , LF, and FF . As a result, the attacker must write a null character before writing the return address to avoid altering the canary. This prevents attacks using strcpy() and other methods that return upon copying

4366-423: The oldest and more reliable methods for attackers to gain unauthorized access to a computer. The canonical method for exploiting a stack-based buffer overflow is to overwrite the function return address with a pointer to attacker-controlled data (usually on the stack itself). This is illustrated with strcpy() in the following example: This code takes an argument from the command line and copies it to

4440-437: The overflow actually occurs within the stack frame for memcpy . However, because the buffer that overflows during the call to memcpy resides in a previous stack frame, the return pointer for memcpy will have a numerically higher memory address than the buffer. This means that instead of the return pointer for foo being overwritten, the return pointer for memcpy will be overwritten. At most, this means that growing

4514-602: The pointer and additional data, describing the region that they point to. Tagging is a compiler-based or hardware-based (requiring a tagged architecture ) technique for tagging the type of a piece of data in memory, used mainly for type checking. By marking certain areas of memory as non-executable, it effectively prevents memory allocated to store data from containing executable code. Also, certain areas of memory can be marked as non-allocated, preventing buffer overflows. Historically, tagging has been used for implementing high-level programming languages; with appropriate support from

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4588-406: The process) the canary value must also be overwritten. This value is checked to make sure it has not changed before a routine uses the return pointer on the stack. This technique can greatly increase the difficulty of exploiting a stack buffer overflow because it forces the attacker to gain control of the instruction pointer by some non-traditional means such as corrupting other important variables on

4662-556: The register window spill/fill routines which makes buffer overflows much more difficult to exploit. It uses a unique hardware feature of the Sun Microsystems SPARC architecture (that being: deferred on-stack in-frame register window spill/fill) to detect modifications of return pointers (a common way for an exploit to hijack execution paths) transparently, automatically protecting all applications without requiring binary or source modifications. The performance impact

4736-777: The result of a signed binary arithmetic operation. If the leftmost retained bit of the result is not the same as the infinite number of digits to the left, then that means overflow occurred. XORing those two bits will give a "1" if there is an overflow. XOR can be used to swap two numeric variables in computers, using the XOR swap algorithm ; however this is regarded as more of a curiosity and not encouraged in practice. XOR linked lists leverage XOR properties in order to save space to represent doubly linked list data structures. In computer graphics , XOR-based drawing methods are often used to manage such items as bounding boxes and cursors on systems without alpha channels or overlay planes. It

4810-446: The return address off the stack and jumps to that address (i.e. starts executing instructions from that address). Thus, the attacker has overwritten the return address with a pointer to the stack buffer char c[12] , which now contains attacker-supplied data. In an actual stack buffer overflow exploit the string of "A"'s would instead be shellcode suitable to the platform and desired function. If this program had special privileges (e.g.

4884-512: The return instruction will return to the payload controlled by the exploiter. Jump Oriented Programming is a technique that uses jump instructions to reuse code instead of ret instruction. A limitation of ASLR realization on 64-bit systems is that it is vulnerable to memory disclosure and information leakage attacks. The attacker can launch the ROP by revealing a single function address using information leakage attack. The following section describes

4958-463: The similar existing strategy for breaking down the ASLR protection. XOR Exclusive or , exclusive disjunction , exclusive alternation , logical non-equivalence , or logical inequality is a logical operator whose negation is the logical biconditional . With two inputs, XOR is true if and only if the inputs differ (one is true, one is false). With multiple inputs, XOR is true if and only if

5032-495: The stack frame. This helped avoid the corruption of pointers, preventing access to arbitrary memory locations. Red Hat engineers identified problems with ProPolice though, and in 2005 re-implemented stack-smashing protection for inclusion in GCC 4.1. This work introduced the -fstack-protector flag, which protects only some vulnerable functions, and the -fstack-protector-all flag, which protects all functions whether they need it or not. In 2012, Google engineers implemented

5106-417: The stack in the opposite direction will change some details of how stack buffer overflows are exploitable, but it will not reduce significantly the number of exploitable bugs. Over the years, a number of control-flow integrity schemes have been developed to inhibit malicious stack buffer overflow exploitation. These may usually be classified into three categories: Stack canaries, named for their analogy to

5180-553: The stack, and in cases where the overflow was triggered by mistake, will often cause the program to crash or operate incorrectly. Stack buffer overflow is a type of the more general programming malfunction known as buffer overflow (or buffer overrun). Overfilling a buffer on the stack is more likely to derail program execution than overfilling a buffer on the heap because the stack contains the return addresses for all active function calls. Stack buffer overflow can be caused deliberately as part of an attack known as stack smashing . If

5254-440: The stack, the attacker can still use the overwritten return address (the instruction pointer) to point to data in a code segment ( .text on Linux) or every other executable section of the program. The goal is to reuse existing code. Consists to overwrite the return pointer a bit before a return instruction (ret in x86) of the program. The instructions between the new return pointer and the return instruction will be executed and

5328-399: The stack. Another approach to preventing stack buffer overflow exploitation is to enforce a memory policy on the stack memory region that disallows execution from the stack ( W^X , "Write XOR Execute"). This means that in order to execute shellcode from the stack an attacker must either find a way to disable the execution protection from memory, or find a way to put their shellcode payload in

5402-406: The way of exploitation. Another attack is the so-called return to libc method for shellcode creation. In this attack the malicious payload will load the stack not with shellcode, but with a proper call stack so that execution is vectored to a chain of standard library calls, usually with the effect of disabling memory execute protections and allowing shellcode to run as normal. This works because

5476-520: The well-known two-element field F 2 {\displaystyle \mathbb {F} _{2}} . This field can represent any logic obtainable with the system ( ∧ , ∨ ) {\displaystyle (\land ,\lor )} and has the added benefit of the arsenal of algebraic analysis tools for fields. More specifically, if one associates F {\displaystyle F} with 0 and T {\displaystyle T} with 1, one can interpret

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