CWE WEAKNESSES  /  CWE-805

CWE-805

Buffer Access with Incorrect Length Value

What it is

The product uses a sequential operation to read or write a buffer, but it uses an incorrect length value that causes it to access memory that is outside of the bounds of the buffer.

When the length value exceeds the size of the destination, a buffer overflow could occur.

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 the buffer is as large as specified.- 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 accessi
• [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
• [Architecture and Design, Operation] Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the product or its environment. For example, database applications rarely need to run as the database adm

Real-world CVE examples

• CVE-2011-1959 — Chain: large length value causes buffer over-read (CWE-126)
• CVE-2011-1848 — Use of packet length field to make a calculation, then copy into a fixed-size buffer
• CVE-2011-0105 — Chain: retrieval of length value from an uninitialized memory location
• CVE-2011-0606 — Crafted length value in document reader leads to buffer overflow
• CVE-2011-0651 — SSL server overflow when the sum of multiple length fields exceeds a given value
• CVE-2010-4156 — Language interpreter API function doesn't validate length argument, leading to information exposure

Related weaknesses

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