JS/PY: do not filter away regular expressions with lookbehinds #6734
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erik-krogh
changed the title
asgerf
approved these changes
Sep 23, 2021
We still don't include lookbehinds in the NFA construction, so a lookbehind will be seen as a rejection (a state with no outgoing transitions), and if it occurs after the pump this could lead to a spurious rejecting suffix being found.
If we wanted to play it safe I'd say we'd need to add a transition which acts as epsilon during rejecting-suffix construction, and as an unmatchable symbol during the pump.
But like you said, it's hard to think of a realistic scenario where this would happen, so I'm ok with leaving it like this for now.
Maybe add a change note?
I don't think this needs a change note. |
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The new result in the tests appears to be a TP (although I'm not sure, it appears to be an invalid RegExp according to V8).
CVE-2021-3795: TP/TN
The original PR that filtered away lookbehinds was the PR that added support for lookbehinds throughout the JavaScript analysis. But no new tests for ReDoS were added back then, so I'm not sure what the motivation was.
I can't think of a realistic way of causing an FP with this change.
Python evaluation looks OK.
JavaScript evaluation looks OK.
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