CVE-2026-77640 — LOW (3.7) — White Hats Nepal

Vulnerability Description

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 Score

3.7

LOW

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

Attack Vector

NETWORK

Attack Complexity

HIGH

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality

NONE

Integrity

NONE

Availability

LOW

Related Weaknesses (CWE)

CWE-1284

References

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

FAQ

What is CVE-2026-77640?

CVE-2026-77640 is a vulnerability with a CVSS score of 3.7 (LOW). 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 n...

How severe is CVE-2026-77640?

CVE-2026-77640 has been rated LOW with a CVSS base score of 3.7/10. Review the CVSS metrics above for detailed severity breakdown.

Is there a patch for CVE-2026-77640?

Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.