Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-471 Base Draft
Modification of Assumed-Immutable Data (MAID)
This vulnerability occurs when an application fails to protect data it assumes cannot be changed, allowing an attacker to alter it.
Definition
What is CWE-471?
This vulnerability occurs when an application fails to protect data it assumes cannot be changed, allowing an attacker to alter it.
Many applications rely on specific pieces of data remaining constant for correct and secure operation. When developers mistakenly treat certain inputs as read-only—like hidden form fields, session cookies, or DNS records—they create a weak spot. Attackers can then modify this assumed-immutable data to bypass security checks, escalate privileges, or corrupt application logic.
This flaw often stems from misplaced trust in client-side controls or external systems. To prevent it, developers must validate all critical data on the server side, regardless of its perceived source or intended immutability. Never rely on client-side mechanisms like hidden fields or cookies to store security-sensitive values without verification.
Real-world impact
Real-world CVEs caused by CWE-471
-
Relies on $PHP_SELF variable for authentication.
-
Gain privileges by modifying assumed-immutable code addresses that are accessed by a driver.
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 Java
In the code excerpt below, an array returned by a Java method is modified despite the fact that arrays are mutable.
String[] colors = car.getAllPossibleColors();
colors[0] = "Red"; 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-471
- Architecture and Design / Operation / Implementation When the data is stored or transmitted through untrusted sources that could modify the data, implement integrity checks to detect unauthorized modification, or store/transmit the data in a trusted location that is free from external influence.
Detection signals
How to detect CWE-471
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.
Plexicus auto-detects CWE-471 and opens a fix PR in under 60 seconds.
Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.
Frequently asked questions What is CWE-471?
How serious is CWE-471?
What languages or platforms are affected by CWE-471?
How can I prevent CWE-471?
How does Plexicus detect and fix CWE-471?
Where can I learn more about CWE-471?
Frequently asked questions
What is CWE-471?
This vulnerability occurs when an application fails to protect data it assumes cannot be changed, allowing an attacker to alter it.
How serious is CWE-471?
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-471?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent CWE-471?
When the data is stored or transmitted through untrusted sources that could modify the data, implement integrity checks to detect unauthorized modification, or store/transmit the data in a trusted location that is free from external influence.
How does Plexicus detect and fix CWE-471?
Plexicus's SAST engine matches the data-flow signature for CWE-471 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-471?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/471.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-471
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