There’s apparently no writeup on exactly what was the fix. So I’m going to make a guess that this is the chromium commit that fixed the problem: https://source.chromium.org/chromium/chromium/src/+/224140d4...

And this commit contained a refactoring from BROTLI_BOOL to BrotliDecoderErrorCode so the situation was that probably one of the error conditions previously simply returned false but needed more detail about what went wrong to continue safely.

Well okay this change from `if (prev_ix < cur_ix)` to `if (prev_ix < cur_ix && cached_backward <= max_backward)` is also suspicious and could be an related or unrelated hardening fix.