Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-627 Variant Incomplete
Dynamic Variable Evaluation
This vulnerability occurs when an application allows user input to directly determine which variable or function name is used at runtime. Without strict validation, an attacker can manipulate these…
Definition
What is CWE-627?
This vulnerability occurs when an application allows user input to directly determine which variable or function name is used at runtime. Without strict validation, an attacker can manipulate these names to access or modify sensitive data, execute unauthorized functions, or disrupt the application's logic.
The core risk lies in the attacker's ability to influence the target of read, write, or execution operations. By injecting crafted variable or function names, they can bypass intended access controls, potentially leading to data exposure, privilege escalation, or arbitrary code execution. The specific impact depends entirely on what variables and functions are within reach of this manipulation.
The severity and nature of the resulting exploit are determined by how the application uses these dynamically evaluated elements. An attacker's control can propagate through the program's data flow, affecting any code paths connected to the compromised variables or functions. Therefore, the damage isn't limited to a single point of injection but can extend to any dependent operations, amplifying the initial breach.
Real-world impact
Real-world CVEs caused by CWE-627
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Chain: Dynamic variable evaluation allows resultant remote file inclusion and path traversal.
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Chain: dynamic variable evaluation in PHP program used to modify critical, unexpected $_SERVER variable for resultant XSS.
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Chain: dynamic variable evaluation in PHP program used to conduct remote file inclusion.
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Dynamic variable evaluation in mail program allows reading and modifying attachments and preferences of other users.
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 pseudo
MITRE has not published a code example for this CWE. The pattern below is illustrative — see Resources for canonical references.
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
// Untrusted input flows directly into the sensitive sink.
return executeUnsafe(input);
} 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-627
- Implementation Refactor the code to avoid dynamic variable evaluation whenever possible.
- Implementation Use only allowlists of acceptable variable or function names.
- Implementation For function names, ensure that you are only calling functions that accept the proper number of arguments, to avoid unexpected null arguments.
Detection signals
How to detect CWE-627
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-627
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-627?
How serious is CWE-627?
What languages or platforms are affected by CWE-627?
How can I prevent CWE-627?
How does Plexicus detect and fix CWE-627?
Where can I learn more about CWE-627?
Frequently asked questions
What is CWE-627?
This vulnerability occurs when an application allows user input to directly determine which variable or function name is used at runtime. Without strict validation, an attacker can manipulate these names to access or modify sensitive data, execute unauthorized functions, or disrupt the application's logic.
How serious is CWE-627?
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-627?
MITRE lists the following affected platforms: PHP, Perl.
How can I prevent CWE-627?
Refactor the code to avoid dynamic variable evaluation whenever possible. Use only allowlists of acceptable variable or function names.
How does Plexicus detect and fix CWE-627?
Plexicus's SAST engine matches the data-flow signature for CWE-627 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-627?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/627.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-627
CWE-914 Parent
Improper Control of Dynamically-Identified Variables
This vulnerability occurs when an application fails to properly secure access to variables whose names are determined at runtime, allowing…
CWE-621 Sibling
Variable Extraction Error
This vulnerability occurs when an application uses unvalidated external input to dynamically select which variables to populate with data.…
CWE-183 Peer
Permissive List of Allowed Inputs
This vulnerability occurs when an application's security filter uses an allowlist that is too broad, mistakenly permitting dangerous…
Resources
Further reading
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