fix: reject value substitution on non-sorry'd definitions - #86
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Compare.loop's dependency walk accepts any constant whose type matches between challenge and solution, even when the value (body) differs. A submitter can exploit this by redefining a non-sorry'd definition to make a false challenge statement true in the solution. Guard the type-only fallback with hasSorryAxValue: only fire when the challenge-side value references sorryAx. Non-sorry definitions with mismatched values are now rejected. Reproducer: https://github.com/savarin/comparator-proof-bypass
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Closing — the vulnerability exists in a local patch, not in upstream master. The type-only fallback this fixes was introduced by our own elaboration-divergence patches, not by upstream code. Apologies for the noise. |
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Fixes: #85
Compare.loopaccepts any dependency whose type matches between challengeand solution, even when the value differs. This allows a submitter to
redefine a non-sorry'd definition to make a false challenge statement true.
Changes
hasSorryAxValue: checks whether aConstantInfo's value expressionreferences
sorryAxviagetUsedConstants.Compare.loop: when a constant's typematches but its value differs, accept only if the challenge-side value
references
sorryAx. Non-sorry definitions with mismatched values arerejected.
Test cases
Reproducer at https://github.com/savarin/comparator-proof-bypass:
test-1-type-mismatch: honest submission → PASS (unchanged)test-2-value-cheat: value substitution → FAIL (was PASS)test-3-sorry-tolerance: sorry'd definition → PASS (unchanged)