Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-1254 Base Draft
Incorrect Comparison Logic Granularity
This vulnerability occurs when a system compares sensitive data, like passwords or authentication tokens, piece-by-piece instead of as a complete unit. If the comparison stops at the first mismatch,…
Definition
What is CWE-1254?
This vulnerability occurs when a system compares sensitive data, like passwords or authentication tokens, piece-by-piece instead of as a complete unit. If the comparison stops at the first mismatch, attackers can measure tiny timing differences to gradually guess the correct value.
Developers often implement comparison logic—for passwords, MACs, or challenge responses—by checking each character or byte individually and exiting early when a mismatch is found. This "short-circuit" behavior creates a detectable timing side-channel: each incorrect guess takes slightly longer to fail as more characters match. An attacker can exploit this by systematically trying different values and analyzing response times to reconstruct the secret, piece by piece.
To prevent this, always use constant-time comparison functions that process the entire input regardless of content. These functions ensure the comparison takes the same amount of time whether it succeeds or fails, eliminating the timing side-channel. Never roll your own comparison for security-critical data; rely on vetted library functions designed to resist timing attacks.
Real-world impact
Real-world CVEs caused by CWE-1254
-
Smartphone OS uses comparison functions that are not in constant time, allowing side channels
-
Java-oriented framework compares HMAC signatures using String.equals() instead of a constant-time algorithm, causing timing discrepancies
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Password-checking function in router terminates validation of a password entry when it encounters the first incorrect character, which allows remote attackers to obtain passwords via a brute-force attack that relies on timing differences in responses to incorrect password guesses, aka a timing side-channel attack.
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-1254
- Implementation The hardware designer should ensure that comparison logic is implemented so as to compare in one operation instead in smaller chunks.
Detection signals
How to detect CWE-1254
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-1254
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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-1254?
How serious is CWE-1254?
What languages or platforms are affected by CWE-1254?
How can I prevent CWE-1254?
How does Plexicus detect and fix CWE-1254?
Where can I learn more about CWE-1254?
Frequently asked questions
What is CWE-1254?
This vulnerability occurs when a system compares sensitive data, like passwords or authentication tokens, piece-by-piece instead of as a complete unit. If the comparison stops at the first mismatch, attackers can measure tiny timing differences to gradually guess the correct value.
How serious is CWE-1254?
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-1254?
MITRE lists the following affected platforms: Not OS-Specific, Not Architecture-Specific, Not Technology-Specific.
How can I prevent CWE-1254?
The hardware designer should ensure that comparison logic is implemented so as to compare in one operation instead in smaller chunks.
How does Plexicus detect and fix CWE-1254?
Plexicus's SAST engine matches the data-flow signature for CWE-1254 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-1254?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/1254.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-1254
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