What is CVE-2026-77640?

CVE-2026-77640 is a low-severity vulnerability in Torproject Tor, classified under Improper Validation of Specified Quantity in Input. CVSS score: 3.7/10. Published 2026-08-20.

How severe is CVE-2026-77640?

Low severity. CVSS v3 base score is 3.7 out of 10.

Vulnerability in Torproject Tor

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 v3 metric

CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L.

Affected products

Torproject Tor

Weakness classification (CWE)

CWE-1284 — Improper Validation of Specified Quantity in Input

References

cve@mitre.org

Frequently asked questions

What is CVE-2026-77640?: CVE-2026-77640 is a low-severity vulnerability in Torproject Tor, classified under Improper Validation of Specified Quantity in Input. CVSS score: 3.7/10. Published 2026-08-20.
How severe is CVE-2026-77640?: Low severity. CVSS v3 base score is 3.7 out of 10.