Verify TSIG MAC before checking timestamp so BadSignature is not pree… - #1293
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adityaanikam wants to merge 1 commit into
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Verify TSIG MAC before checking timestamp so BadSignature is not pree…#1293adityaanikam wants to merge 1 commit into
adityaanikam wants to merge 1 commit into
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jschlyter
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Aug 16, 2026
| now = int(time.time()) | ||
| wrong_key = dns.tsig.Key(keyname, "abcd", "hmac-sha256") | ||
| with self.assertRaises(dns.tsig.BadSignature): | ||
| dns.tsig.validate(w, wrong_key, keyname, tsig, now + 1000, b"", tsig_start) |
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Explicitly declaring and using a wrong_key might increase readability.
jschlyter
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Aug 16, 2026
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Looking good. I've also read the RFCs and agree with the change.
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Closes #1287.
validate() checked the timestamp before verifying the MAC, so a request with both a bad signature and a bad timestamp reported BadTime instead of BadSignature, RFC 8945 5.2 expects MAC validity to be established first. rthalley confirmed following the RFC is the right call here, with the behavior change noted in a release note rather than treated as something needing extra caution.
The reorder itself is a two line move, no other logic changed. The existing test_validate had a latent issue that only surfaced once the ordering changed: its BadTime case used a key with a different secret than the one that actually signed the message, so the MAC would also fail, but the old ordering never reached that check, checking time first meant it never mattered. I fixed that case to use the correct signing key so it isolates a genuine timestamp-only failure, and added a new test for the actual scenario from the issue, a bad MAC combined with a bad timestamp now correctly raises BadSignature.