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Weakness (CWE)

CWE-805: Buffer Access with Incorrect Length Value

Base Incomplete

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.

How to prevent it (8 mitigations)

  1. 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 a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.

  2. 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.

  3. 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] discusses canary-based detection in detail.

  4. 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 accessing the buffer in a loop and make sure there is no danger of writing past the allocated space.

    - If necessary, truncate all input strings to a reasonable length before passing them to the copy and concatenation functions.

  5. 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.

  6. 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]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as "rebasing" (for Windows) and "prelinking" (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.

    For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].

  7. 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 Execution Prevention) from D3FEND [REF-1336].

  8. 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 administrator, especially in day-to-day operations.

Source: MITRE CWE-805

All Critical High Medium Low Exploited only Public exploit

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