CVE-2026-77640

tor before 0.4.9.9 was prone to an infinite loop when decompressing a truncated zlib/gzip stream with done=1. A truncated stream never reaches Z_STREAM_END, causing zlib to return Z_BUF_ERROR with no input remaining, which buf_add_compress() mistook for a full output buffer and retried forever. Fixed by returning TOR_COMPRESS_ERROR in that case so the caller can abort cleanly. This is TROVE-2026-021.

CVSS 3.1

5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS

0.4% chance of exploitation in the next 30 days; higher than 31% of CVEs (scores of 2026-10-25)

CWE

CWE-1284

Published

2026-08-20

Modified

2026-10-18

Record from

the NVD, synced 2026-10-19

Affected

• torproject:tor

References

• https://gitlab.torproject.org/tpo/core/tor/-/raw/tor-0.4.9.9/ChangeLog

Check your stackJSON