CVE-2026-77638: CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') in torproject Tor
A race condition vulnerability exists in Tor versions before 0.4.9.11 that could allow a rendezvous point to impersonate an onion service during client connection attempts. This flaw involves improper synchronization leading to concurrent execution issues. The vulnerability has a high severity rating with a CVSS score of 8.9.
AI Analysis
Technical Summary
CVE-2026-77638 is a race condition vulnerability (CWE-362) in Tor prior to version 0.4.9.11. Under specific timing conditions, a rendezvous point could man-in-the-middle the connection by impersonating the onion service the client intends to reach. This occurs due to improper synchronization in handling shared resources, allowing concurrent execution that leads to this impersonation attack. The vulnerability affects versions from 0.3.5.3-alpha up to but not including 0.4.9.11.
Potential Impact
Successful exploitation allows an attacker controlling a rendezvous point to impersonate the onion service, potentially intercepting or altering communications. This compromises confidentiality and integrity of the Tor hidden service connection. The vulnerability has a low impact on availability.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. No official fix or patch link is provided in the available data. Users should monitor torproject advisories for updates and apply any official patches once released.
CVE-2026-77638: CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') in torproject Tor
Description
A race condition vulnerability exists in Tor versions before 0.4.9.11 that could allow a rendezvous point to impersonate an onion service during client connection attempts. This flaw involves improper synchronization leading to concurrent execution issues. The vulnerability has a high severity rating with a CVSS score of 8.9.
CVSS v3.1
Score 8.9high
Affected software
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 race condition vulnerability (CWE-362) in Tor prior to version 0.4.9.11. Under specific timing conditions, a rendezvous point could man-in-the-middle the connection by impersonating the onion service the client intends to reach. This occurs due to improper synchronization in handling shared resources, allowing concurrent execution that leads to this impersonation attack. The vulnerability affects versions from 0.3.5.3-alpha up to but not including 0.4.9.11.
Potential Impact
Successful exploitation allows an attacker controlling a rendezvous point to impersonate the onion service, potentially intercepting or altering communications. This compromises confidentiality and integrity of the Tor hidden service connection. The vulnerability has a low impact on availability.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. No official fix or patch link is provided in the available data. Users should monitor torproject advisories for updates and apply any official patches once released.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- mitre
- Date Reserved
- 2026-08-20T20:52:29.384Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a876c9aacd9273b4920be00
Added to database: 08/20/2026, 21:07:38 UTC
Last enriched: 08/20/2026, 21:22:05 UTC
Last updated: 08/20/2026, 22:28:05 UTC
Views: 5
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
External Links
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.