What is CVE-2026-77638?

CVE-2026-77638 is a high-severity vulnerability in Torproject Tor, classified under Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). CVSS score: 8.9/10. Published 2026-08-20.

How severe is CVE-2026-77638?

High severity. CVSS v3 base score is 8.9 out of 10.

Vulnerability in Torproject Tor

CVE-2026-77638

Tor before 0.4.9.11 is prone to a race condition where in just the right circumstances a rendezvous point could man-in-the-middle (impersonate) the onion service that the client was trying to reach.

Vulnerability class: Race Condition

CVSS v3 metric

CVSS v3 base score 8.9 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L.

Affected products

Torproject Tor

Weakness classification (CWE)

CWE-362 — Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition)

References

cve@mitre.org

Frequently asked questions

What is CVE-2026-77638?: CVE-2026-77638 is a high-severity vulnerability in Torproject Tor, classified under Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). CVSS score: 8.9/10. Published 2026-08-20.
How severe is CVE-2026-77638?: High severity. CVSS v3 base score is 8.9 out of 10.