CWE-793: Only Filtering One Instance of a Special Element | Glexia
CWE-793 (Only Filtering One Instance of a Special Element) weakness overview with consequences, detection methods, mitigations, related CVEs and MITRE ATT&CK…
Glexia's Take · Automated analysis
CWE-793: Only Filtering One Instance of a Special Element
Only Filtering One Instance of a Special Element represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Executive Impact
- Integrity: Unexpected State
Developer Pattern
CWE-793 is the kind of defect developers can usually prevent with explicit validation, safer framework defaults, and tests that exercise hostile input or unsafe state transitions.
Automation confidence
high confidence from CWE-793, 4.20.
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Official CWE Definition
CWE-793: Only Filtering One Instance of a Special Element
The product receives data from an upstream component, but only filters a single instance of a special element before sending it to a downstream component.
Incomplete filtering of this nature may be location-dependent, as in only the first or last element is filtered.
Developer And Remediation Guidance
How teams prevent and detect this weakness
Causes
- The following code takes untrusted input and uses a regular expression to filter "../" from the input. It then appends this result to the /home/user/ directory and attempts to read the file in the final resulting path. Since the regular expression does not have the /g global match modifier, it only removes the first instance of "../" it comes across. So an input value such as:,will have the first "../" stripped, resulting in:,This value is then concatenated with the /home/user/ directory:,which causes the /etc/passwd file to be retrieved once the operating system has resolved the ../ sequences in the pathname. This leads to relative path traversal (CWE-23).
Remediation
- Use safe APIs
- Centralize the control
- Add regression tests
- Review logs and telemetry for attempted abuse
Detection
- Code review
- SAST
- DAST
- Focused regression tests
Mappings
Related CVEs, CWEs, and ATT&CK context
ATT&CK Relevance
ATT&CK relevance is shown only when reviewed or responsibly inferred.