CWE-131 Detail

The product does not correctly calculate the size to be used when allocating a buffer, which could lead to a buffer overflow.

Modes Of Introduction

Implementation

Applicable Platforms

Language

Name: C (Undetermined)
Name: C++ (Undetermined)

Common Consequences

Observed Examples

Potential Mitigations

Phases : Implementation
When allocating a buffer for the purpose of transforming, converting, or encoding an input, allocate enough memory to handle the largest possible encoding. For example, in a routine that converts "&" characters to "&" for HTML entity encoding, the output buffer needs to be at least 5 times as large as the input buffer.
Phases : Implementation

Understand the programming language's underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, "not-a-number" calculations, and how the language handles numbers that are too large or too small for its underlying representation. [REF-7]

Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.

Phases : Implementation
Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.
Phases : 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.
Phases : Implementation
When processing structured incoming data containing a size field followed by raw data, identify and resolve any inconsistencies between the size field and the actual size of the data (CWE-130).
Phases : Implementation
When allocating memory that uses sentinels to mark the end of a data structure - such as NUL bytes in strings - make sure you also include the sentinel in your calculation of the total amount of memory that must be allocated.
Phases : Implementation
Replace unbounded copy functions with analogous functions that support length arguments, such as strcpy with strncpy. Create these if they are not available.
Phases : Implementation
Use sizeof() on the appropriate data type to avoid CWE-467.
Phases : Implementation
Use the appropriate type for the desired action. For example, in C/C++, only use unsigned types for values that could never be negative, such as height, width, or other numbers related to quantity. This will simplify validation and will reduce surprises related to unexpected casting.
Phases : 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.

Use libraries or frameworks that make it easier to handle numbers without unexpected consequences, or buffer allocation routines that automatically track buffer size.

Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++). [REF-106]

Phases : 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.

Phases : 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].

Phases : 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].

Phases : Implementation
Examine compiler warnings closely and eliminate problems with potential security implications, such as signed / unsigned mismatch in memory operations, or use of uninitialized variables. Even if the weakness is rarely exploitable, a single failure may lead to the compromise of the entire system.
Phases : 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 software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.
Phases : Architecture and Design // Operation

Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software.

OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations.

This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise.

Be careful to avoid CWE-243 and other weaknesses related to jails.

Detection Methods

Automated Static Analysis

This weakness can often be detected using automated static analysis tools. Many modern tools use data flow analysis or constraint-based techniques to minimize the number of false positives.

Automated static analysis generally does not account for environmental considerations when reporting potential errors in buffer calculations. This can make it difficult for users to determine which warnings should be investigated first. For example, an analysis tool might report buffer overflows that originate from command line arguments in a program that is not expected to run with setuid or other special privileges.

Effectiveness : High

Automated Dynamic Analysis

This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.
Effectiveness : Moderate

Manual Analysis

Manual analysis can be useful for finding this weakness, but it might not achieve desired code coverage within limited time constraints. This becomes difficult for weaknesses that must be considered for all inputs, since the attack surface can be too large.

Manual Analysis

This weakness can be detected using tools and techniques that require manual (human) analysis, such as penetration testing, threat modeling, and interactive tools that allow the tester to record and modify an active session.

Specifically, manual static analysis is useful for evaluating the correctness of allocation calculations. This can be useful for detecting overflow conditions (CWE-190) or similar weaknesses that might have serious security impacts on the program.

Effectiveness : High

Automated Static Analysis - Binary or Bytecode

According to SOAR, the following detection techniques may be useful:

Effectiveness : High

Manual Static Analysis - Binary or Bytecode

According to SOAR, the following detection techniques may be useful:

Effectiveness : SOAR Partial

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Effectiveness : SOAR Partial

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Effectiveness : High

Architecture or Design Review

According to SOAR, the following detection techniques may be useful:

Effectiveness : High

Vulnerability Mapping Notes

Justification : This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comment : Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

Related Attack Patterns

NotesNotes

This is a broad category. Some examples include:

• simple math errors,
• incorrectly updating parallel counters,
• not accounting for size differences when "transforming" one input to another format (e.g. URL canonicalization or other transformation that can generate a result that's larger than the original input, i.e. "expansion").

This level of detail is rarely available in public reports, so it is difficult to find good examples.

This weakness may be a composite or a chain. It also may contain layering or perspective differences.

This issue may be associated with many different types of incorrect calculations (CWE-682), although the integer overflow (CWE-190) is probably the most prevalent. This can be primary to resource consumption problems (CWE-400), including uncontrolled memory allocation (CWE-789). However, its relationship with out-of-bounds buffer access (CWE-119) must also be considered.

References

REF-106

SafeInt
David LeBlanc, Niels Dekker.
http://safeint.codeplex.com/

REF-107

Top 25 Series - Rank 18 - Incorrect Calculation of Buffer Size
Jason Lam.
http://software-security.sans.org/blog/2010/03/19/top-25-series-rank-18-incorrect-calculation-of-buffer-size

REF-58

Address Space Layout Randomization in Windows Vista
Michael Howard.
https://learn.microsoft.com/en-us/archive/blogs/michael_howard/address-space-layout-randomization-in-windows-vista

REF-61

Understanding DEP as a mitigation technology part 1
Microsoft.
https://msrc.microsoft.com/blog/2009/06/understanding-dep-as-a-mitigation-technology-part-1/

REF-60

PaX
https://en.wikipedia.org/wiki/Executable_space_protection#PaX

REF-76

Least Privilege
Sean Barnum, Michael Gegick.
https://web.archive.org/web/20211209014121/https://www.cisa.gov/uscert/bsi/articles/knowledge/principles/least-privilege

REF-7

Writing Secure Code
Michael Howard, David LeBlanc.
https://www.microsoftpressstore.com/store/writing-secure-code-9780735617223

REF-44

24 Deadly Sins of Software Security
Michael Howard, David LeBlanc, John Viega.

REF-62

The Art of Software Security Assessment
Mark Dowd, John McDonald, Justin Schuh.

REF-64

Position Independent Executables (PIE)
Grant Murphy.
https://www.redhat.com/en/blog/position-independent-executables-pie

REF-1332

Prelink and address space randomization
John Richard Moser.
https://lwn.net/Articles/190139/

REF-1333

Jump Over ASLR: Attacking Branch Predictors to Bypass ASLR
Dmitry Evtyushkin, Dmitry Ponomarev, Nael Abu-Ghazaleh.
http://www.cs.ucr.edu/~nael/pubs/micro16.pdf

REF-1334

Stack Frame Canary Validation (D3-SFCV)
D3FEND.
https://d3fend.mitre.org/technique/d3f:StackFrameCanaryValidation/

REF-1335

Segment Address Offset Randomization (D3-SAOR)
D3FEND.
https://d3fend.mitre.org/technique/d3f:SegmentAddressOffsetRandomization/

REF-1336

Process Segment Execution Prevention (D3-PSEP)
D3FEND.
https://d3fend.mitre.org/technique/d3f:ProcessSegmentExecutionPrevention/

REF-1337

Bypassing Browser Memory Protections: Setting back browser security by 10 years
Alexander Sotirov and Mark Dowd.
https://www.blackhat.com/presentations/bh-usa-08/Sotirov_Dowd/bh08-sotirov-dowd.pdf

Submission

Modifications