CWE WEAKNESSES  /  CWE-120

CWE-120

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

What it is

The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer.

Impact

Mitigations

• [Requirements]Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.Be wary that
• [Architecture and Design]Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.
• [Operation, Build and Compilation]Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] dis
• [Implementation]Consider adhering to the following rules when allocating and managing an application's memory:- Double check that your buffer is as large as you specify.- When using functions that accept a number of bytes to copy, such as strncpy(), be aware that if the destination buffer size is equal to the source buffer size, it may not NULL-terminate the string.- Check buffer boundaries if acce
• [Implementation]Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.When performing input validation, consider all potentially relevant properties, including length, type of input, the full r
• [Architecture and Design] For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
• [Operation, Build and Compilation]Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Im
• [Operation]Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment.For more information on these techniques see D3-PSEP (Process Segment

Real-world CVE examples

• CVE-2000-1094 — buffer overflow using command with long argument
• CVE-1999-0046 — buffer overflow in local program using long environment variable
• CVE-2002-1337 — buffer overflow in comment characters, when product increments a counter for a ">" but does not decrement for "<"
• CVE-2003-0595 — By replacing a valid cookie value with an extremely long string of characters, an attacker may overflow the application's buffers.
• CVE-2001-0191 — By replacing a valid cookie value with an extremely long string of characters, an attacker may overflow the application's buffers.

Related weaknesses

Source: MITRE CWE. View on cwe.mitre.org →