Reject invalid DEFLATE HLIT values (GH #1368) - #1371
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Inflator::DecodeHeader() accepted HLIT values 30 and 31, although RFC 1951 limits the field to 0 through 29. With HLIT and HDIST both set to 31, the declared code-length total reaches 320 entries against a 318-entry table. The repeat-run guard checked only against that declared total, allowing an out-of-bounds write. HDIST values 30 and 31 remain valid. RFC 1951 permits all 32 distance code lengths, and CreateFixedDistanceDecoder() initialises all 32 entries. Reject invalid HLIT values before filling the table and bound repeat runs against both the declared total and the table capacity.
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Thanks @afldl and @Coralesoft. |
Coralesoft
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Upstream merged the HLIT fix in weidai11/cryptopp#1371, then added a debug assertion for the rejected range, `const` qualifiers, and a 320-entry `codeLengths` buffer matching zlib. Mirror those changes and recognise `-DCRYPTOPP_DEBUG` in the GNUmakefile debug filter to keep our inflator aligned with upstream. The runtime guard already rejects invalid HLIT values, so release behaviour is unchanged.
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Fixes #1368.
Inflator::DecodeHeader()accepted HLIT values 30 and 31, although RFC 1951 limits the field to 0 through 29. With HLIT and HDIST both set to 31, the declared code-length total reaches 320 entries against the 318-entry table. The existing guard checked only against that declared total, allowing an out-of-bounds write.HDIST is left unchanged. RFC 1951 allows up to 32 distance code lengths, and once HLIT is limited to 29 the combined total cannot exceed the table capacity.
The supplied malformed stream is rejected by both the unfixed and fixed builds, so the final result alone does not distinguish them. Instrumentation on master shows the final fill reaching
[276,319), past the 318-entry table. With this change, the invalid header is rejected before the fill loop runs.