CVE-2026-77638

Received Received - Intake

Tor 0.4.9.11 Race Condition in Onion Service Authentication

Publication date: 2026-08-20

Last updated on: 2026-08-20

Assigner: MITRE

Description

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.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-08-20

Last Modified

2026-08-20

Generated

2026-08-21

AI Q&A

2026-08-21

EPSS Evaluated

N/A

NVD

CVE-2026-77638

Affected Vendors & Products

Vendor	Product	Version / Range
tor_project	tor	to 0.4.9.11 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-362	The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

Attack-Flow Graph

Executive Summary

This vulnerability is a race condition in Tor before version 0.4.9.11 that allows a malicious rendezvous point to impersonate an onion service during client connections.

Impact Analysis

An attacker could intercept and impersonate onion services, potentially leading to unauthorized access to sensitive data or services you intended to connect to securely.

Compliance Impact

This vulnerability could lead to unauthorized data exposure or service impersonation, potentially violating confidentiality requirements in GDPR and HIPAA.

Mitigation Strategies

Update Tor to version 0.4.9.11 or later to address the race condition vulnerability.

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