Out-of-bounds read in `train_from_buffer` when sample sizes overflow

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`ZDICT_trainFromBuffer` is never told the length of the samples buffer, so `train_from_buffer` checked that the sample sizes add up to it. With overflow checks off, as in release builds, that sum wrapped around: sizes totalling 2^64 plus the buffer length passed the check, and the trainer read past the end of the buffer. `zstd::dict::from_continuous` relies on this check from zstd 0.4.10; older versions of zstd had their own, covered by a separate advisory. This requires the sample sizes to come from an untrusted source. The flaw was corrected by summing the sizes with overflow checks.

Source published

16 Oct 2026 12:00:00 UTC

Source modified

26 Oct 2026 14:00:04 UTC

Observed here

26 Oct 2026 14:35:44 UTC

Source terms

OSV · upstream source license applies

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