Onion service impersonation via rendezvous race
Published Aug 20, 2026 · Updated Aug 20, 2026
Race condition in The Tor Project Tor before 0.4.9.11 allows attackers to impersonate an onion service via a malicious rendezvous point. Tor's June 25, 2026 changelog narrows the flaw to onion-service rendezvous handling and says the fix prevents a rendezvous point from winning the service-authenticity race, but it does not disclose the affected function or synchronization mistake. Exploitation requires control of the rendezvous point selected for the client connection and can expose or alter client traffic to the intended onion service, with only limited availability impact reported.
Summary
What happened
Race condition in The Tor Project Tor before 0.4.9.11 allows attackers to impersonate an onion service via a malicious rendezvous point. Tor's June 25, 2026 changelog narrows the flaw to onion-service rendezvous handling and says the fix prevents a rendezvous point from winning the service-authenticity race, but it does not disclose the affected function or synchronization mistake. Exploitation requires control of the rendezvous point selected for the client connection and can expose or alter client traffic to the intended onion service, with only limited availability impact reported.
The record
- CVE
- CVE-2026-77638
- Published
- Aug 20, 2026
- Updated
- Aug 20, 2026
- Vendor
- The Tor Project
- Product
- Tor
- Classifications
- CWE-362, T1557
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 20, 2026CVE publishedPublication date reported by the CVE source.
- Aug 20, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0.3.5.3-alpha <0.4.9.11
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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