Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-785 Variant Incomplete
Use of Path Manipulation Function without Maximum-sized Buffer
This vulnerability occurs when a program uses a path manipulation function but supplies an output buffer that is too small to hold the maximum possible path length, such as PATH_MAX.
Definition
What is CWE-785?
This vulnerability occurs when a program uses a path manipulation function but supplies an output buffer that is too small to hold the maximum possible path length, such as PATH_MAX.
When functions like realpath(), readlink(), or PathAppend() are called with a buffer smaller than the maximum possible path size, a buffer overflow can happen. This overflow can corrupt adjacent memory, crash the application, or create opportunities for attackers to execute arbitrary code.
To prevent this, developers should always ensure the output buffer for any path operation is sized to accommodate the system's maximum path length. Using dynamic allocation or verified, platform-specific constants for buffer size is a critical security practice during file and path operations.
Real-world impact
Real-world CVEs caused by CWE-785
No public CVE references are linked to this CWE in MITRE's catalog yet.
How attackers exploit it
Step-by-step attacker path
- 1
Identify a code path that handles untrusted input without validation.
- 2
Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.
- 3
Deliver the payload through a normal request and observe the application's reaction.
- 4
Iterate until the response leaks data, executes attacker code, or escalates privileges.
Vulnerable code example
Vulnerable C
In this example the function creates a directory named "output\" in the current directory and returns a heap-allocated copy of its name.
char *createOutputDirectory(char *name) {
char outputDirectoryName[128];
if (getCurrentDirectory(128, outputDirectoryName) == 0) {
return null;
}
if (!PathAppend(outputDirectoryName, "output")) {
return null;
}
if (!PathAppend(outputDirectoryName, name)) {
return null;
}
if (SHCreateDirectoryEx(NULL, outputDirectoryName, NULL) != ERROR_SUCCESS) {
return null;
}
return StrDup(outputDirectoryName);
} Secure code example
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist
How to prevent CWE-785
- Implementation Always specify output buffers large enough to handle the maximum-size possible result from path manipulation functions.
Detection signals
How to detect CWE-785
Run dynamic application security testing against the live endpoint.
Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.
Code review: flag any new code that handles input from this surface without using the validated framework helpers.
CWE-785
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Frequently asked questions What is CWE-785?
How serious is CWE-785?
What languages or platforms are affected by CWE-785?
How can I prevent CWE-785?
How does Plexicus detect and fix CWE-785?
Where can I learn more about CWE-785?
Frequently asked questions
What is CWE-785?
This vulnerability occurs when a program uses a path manipulation function but supplies an output buffer that is too small to hold the maximum possible path length, such as PATH_MAX.
How serious is CWE-785?
MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.
What languages or platforms are affected by CWE-785?
MITRE lists the following affected platforms: C, C++.
How can I prevent CWE-785?
Always specify output buffers large enough to handle the maximum-size possible result from path manipulation functions.
How does Plexicus detect and fix CWE-785?
Plexicus's SAST engine matches the data-flow signature for CWE-785 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-785?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/785.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-785
Resources
Further reading
- MITRE — official CWE-785 https://cwe.mitre.org/data/definitions/785.html
- Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors https://samate.nist.gov/SSATTM_Content/papers/Seven%20Pernicious%20Kingdoms%20-%20Taxonomy%20of%20Sw%20Security%20Errors%20-%20Tsipenyuk%20-%20Chess%20-%20McGraw.pdf
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