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CWE-794: Incomplete Filtering of Multiple Instances of… | Glexia

CWE-794 (Incomplete Filtering of Multiple Instances of Special Elements) weakness overview with consequences, detection methods, mitigations, related CVEs and…

Release 4.20weaknessIncomplete
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Glexia's Take · Automated analysis

CWE-794: Incomplete Filtering of Multiple Instances of Special Elements

Incomplete Filtering of Multiple Instances of Special Elements 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-794 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-794, 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-794: Incomplete Filtering of Multiple Instances of Special Elements

The product receives data from an upstream component, but does not filter all instances of a special element before sending it to a downstream component.

Type
weakness
Abstraction
Variant
Status
Incomplete
Source
MITRE CWE definition

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

Related CWEs

Related CVEs

Related CVE mappings appear after CVE records are cross-indexed.

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ATT&CK Relevance

ATT&CK relevance is shown only when reviewed or responsibly inferred.