Detect timing-unsafe secret comparisons via taint analysis (CWE-208)#576
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Detect timing-unsafe secret comparisons via taint analysis (CWE-208)#576
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Pull request overview
Adds a new taint-analysis rule to detect timing-unsafe secret comparisons (CWE-208) by introducing taint sinks at ==/===/!=/!== and strcmp()/strcasecmp() usage, plus PHPT coverage to validate secret vs non-secret behavior.
Changes:
- Register a new
TimingUnsafeComparisonHandlerhook in the plugin. - Implement sink insertion for comparison operators and timing-unsafe string compare functions when
--taint-analysisis active. - Add 11 taint-analysis type tests covering user/system secret flows, operand position, indirect flow, and safe scenarios (
hash_equals, non-secret comparisons).
Reviewed changes
Copilot reviewed 13 out of 13 changed files in this pull request and generated 5 comments.
Show a summary per file
| File | Description |
|---|---|
| src/Plugin.php | Registers the new rule handler with Psalm’s plugin hook system. |
| src/Handlers/Rules/TimingUnsafeComparisonHandler.php | Implements taint sink creation for timing-unsafe comparisons involving user_secret/system_secret. |
| tests/Type/tests/TaintAnalysis/TaintedUserSecretTimingComparison.phpt | Asserts == comparison against a user_secret triggers TaintedUserSecret. |
| tests/Type/tests/TaintAnalysis/TaintedUserSecretStrcasecmp.phpt | Asserts strcasecmp() against a user_secret triggers TaintedUserSecret. |
| tests/Type/tests/TaintAnalysis/TaintedUserSecretNotEqualComparison.phpt | Asserts != comparison against a user_secret triggers TaintedUserSecret. |
| tests/Type/tests/TaintAnalysis/TaintedUserSecretLeftOperand.phpt | Asserts detection works when the secret is on the left operand. |
| tests/Type/tests/TaintAnalysis/TaintedSystemSecretTimingComparison.phpt | Asserts === comparison against a system_secret triggers TaintedSystemSecret. |
| tests/Type/tests/TaintAnalysis/TaintedSystemSecretStrcmp.phpt | Asserts strcmp() against a system_secret triggers TaintedSystemSecret. |
| tests/Type/tests/TaintAnalysis/TaintedSystemSecretNotIdenticalComparison.phpt | Asserts !== comparison against a system_secret triggers TaintedSystemSecret. |
| tests/Type/tests/TaintAnalysis/TaintedSystemSecretIndirectComparison.phpt | Asserts secret taint propagates through variables before comparison. |
| tests/Type/tests/TaintAnalysis/SafeNonSecretStrcmp.phpt | Ensures strcmp() with non-secret input does not trigger secret issues. |
| tests/Type/tests/TaintAnalysis/SafeNonSecretComparison.phpt | Ensures === with non-secret input does not trigger secret issues. |
| tests/Type/tests/TaintAnalysis/SafeHashEqualsSecret.phpt | Ensures hash_equals() with a secret does not trigger timing-unsafe comparison issues. |
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Add TimingUnsafeComparisonHandler that creates taint sinks at ===, ==, !==, !=, strcmp(), and strcasecmp() for USER_SECRET and SYSTEM_SECRET taint types. When a secret-tainted value flows into a timing-unsafe comparison, Psalm emits TaintedUserSecret or TaintedSystemSecret. Closes #570
Reduces taint graph size and avoids duplicate reports when an operand has multiple parent nodes (unions/merged values). One sink is created per comparison side, with all parent nodes connected to it via addPath.
Better DX — the list is scannable and easy to extend.
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Blocked by vimeo/psalm#11762
What does this PR do?
Adds
TimingUnsafeComparisonHandlerthat detects timing-unsafe string comparisons involving secrets. When values tainted withuser_secretorsystem_secretflow into===,==,!==,!=,strcmp(), orstrcasecmp(), Psalm emitsTaintedUserSecretorTaintedSystemSecret.The handler works by adding taint sinks at comparison operators during expression analysis. Only activates during
--taint-analysisruns; near-zero overhead in normal analysis.Use
hash_equals()for constant-time comparison instead.Closes #570