CVE-2026-77639 — MEDIUM (5.3)

Vulnerability Description

Tor before 0.4.9.9 was prone to a compression bomb bypass where an attacker could concatenate many gzip or zlib sub-streams, each just under the per-stream detection threshold, to avoid the compression bomb check entirely. This is TROVE-2026-022.

CVSS Score

5.3

MEDIUM

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

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality

NONE

Integrity

NONE

Availability

LOW

Related Weaknesses (CWE)

CWE-420

References

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

FAQ

What is CVE-2026-77639?

CVE-2026-77639 is a vulnerability with a CVSS score of 5.3 (MEDIUM). Tor before 0.4.9.9 was prone to a compression bomb bypass where an attacker could concatenate many gzip or zlib sub-streams, each just under the per-stream detection threshold, to avoid the compressio...

How severe is CVE-2026-77639?

CVE-2026-77639 has been rated MEDIUM with a CVSS base score of 5.3/10. Review the CVSS metrics above for detailed severity breakdown.

Is there a patch for CVE-2026-77639?

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