CVE-2026-77638: CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') in torproject Tor
Description
A race condition vulnerability (CWE-362) exists in Tor versions from 0.3.5.3-alpha up to but not including 0.4.9.11. This flaw allows a rendezvous point to potentially man-in-the-middle and impersonate the onion service a client is attempting to reach. The vulnerability has a high severity with a CVSS score of 8.9.
CVSS v3.1
Score 8.9high
Affected software
torproject
Tor
pkg:github/torproject/torRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-77638 is a concurrency issue in Tor before version 0.4.9.11 where improper synchronization leads to a race condition. Under specific conditions, this flaw enables a rendezvous point to impersonate an onion service, effectively performing a man-in-the-middle attack against the client. The vulnerability affects versions >=0.3.5.3-alpha and <0.4.9.11. The CVSS 3.1 score is 8.9, indicating high impact on confidentiality and integrity with low availability impact.
Potential Impact
Successful exploitation allows an attacker controlling a rendezvous point to impersonate the onion service the client intends to reach, compromising confidentiality and integrity of communications. This could lead to interception or manipulation of data exchanged between the client and the onion service.
Mitigation Recommendations
Upgrade Tor to version 0.4.9.11 or later, where this race condition vulnerability is fixed. No other mitigation or temporary workaround is indicated. Users should apply the official fix to prevent exploitation.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- mitre
- Date Reserved
- 2026-08-20T20:52:29.384Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6a876c9aacd9273b4920be00
Added to database: 08/20/2026, 21:07:38 UTC
Last enriched: 09/10/2026, 22:47:33 UTC
Last updated: 10/04/2026, 18:53:18 UTC
Views: 72
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