CWE-787 Detail

The product writes data past the end, or before the beginning, of the intended buffer.

Modes Of Introduction

Implementation

Applicable Platforms

Language

Name: C (Often)
Name: C++ (Often)
Class: Assembly (Undetermined)

Technologies

Class: ICS/OT (Often)

Common Consequences

Observed Examples

Potential Mitigations

Phases : 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.

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.

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.

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 : 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.

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
Replace unbounded copy functions with analogous functions that support length arguments, such as strcpy with strncpy. Create these if they are not available.

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 out-of-bounds memory operations. 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.

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.

References

REF-1029

Smashing The Stack For Fun And Profit
Aleph One.
http://phrack.org/issues/49/14.html

REF-7

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

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-62

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

REF-90

Buffer UNDERFLOWS: What do you know about it?
https://seclists.org/vuln-dev/2004/Jan/22

REF-56

Using the Strsafe.h Functions
Microsoft.
https://learn.microsoft.com/en-us/windows/win32/menurc/strsafe-ovw?redirectedfrom=MSDN

REF-57

Safe C String Library v1.0.3
Matt Messier, John Viega.
http://www.gnu-darwin.org/www001/ports-1.5a-CURRENT/devel/safestr/work/safestr-1.0.3/doc/safestr.html

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-60

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

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-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