CWE-621

Variant Abstraction Level
Pillar — Highest-level weakness category
Class — Abstract, language-independent
Base — Specific enough to detect
Variant — Tied to specific technology
Compound — Requires multiple weaknesses Incomplete MITRE CWE Status
Stable — Fully reviewed and complete
Draft — Under development, may change
Incomplete — Partially defined by MITRE
Deprecated — No longer recommended
Obsolete — Replaced by another CWE
Variable Extraction Error

Description

The product uses external input to determine the names of variables into which information is extracted, without verifying that the names of the specified variables are valid. This could cause the program to overwrite unintended variables.

For example, in PHP, extraction can be used to provide functionality similar to register_globals, a dangerous functionality that is frequently disabled in production systems. Calling extract() or import_request_variables() without the proper arguments could allow arbitrary global variables to be overwritten, including superglobals. Similar functionality is possible in other interpreted languages, including custom languages.

Consequences

Integrity — Modify Application Data

An attacker could modify sensitive data or program variables.

Mitigations

Phase: Implementation

Use allowlists of variable names that can be extracted.

Phase: Implementation

Consider refactoring your code to avoid extraction routines altogether.

Phase: Implementation

In PHP, call extract() with options such as EXTR_SKIP and EXTR_PREFIX_ALL; call import_request_variables() with a prefix argument. Note that these capabilities are not present in all PHP versions.