Description
Tor before 0.4.9.12 interprets the CC_RESPONSE extension even when CC_REQUEST was not sent, which allows remote attackers to cause a denial of service (crash) because of corrupted congestion-control state. This is TROVE-2026-032.
Published: 2026-09-09
Score: 6.5 Medium
EPSS: < 1% Very Low
KEV: No
Impact: Denial of Service
Action: Patch
AI Analysis

Impact

Tor before version 0.4.9.12 interprets a CC_RESPONSE extension even when a CC_REQUEST was not previously sent, corrupting the congestion-control state and causing the process to crash. This flaw yields a denial‑of‑service for the Tor daemon and can interrupt the functioning of Tor circuits that rely on that controller.

Affected Systems

The Tor daemon released by the Tor Project with versions earlier than 0.4.9.12 is affected, as the bug exists in the codebase up to and including 0.4.9.11.

Risk and Exploitability

The CVSS score of 6.5 indicates a moderate severity vulnerability. The EPSS score is not available, and the vulnerability is not listed in CISA’s KEV catalog, implying no widespread exploitation has been documented. The likely attack vector is remote, whereby an attacker can transmit a malformed CC_RESPONSE packet over the network to trigger the crash.

Generated by OpenCVE AI on September 9, 2026 at 04:28 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade the Tor installation to version 0.4.9.12 or newer, which removes the buggy CC_RESPONSE handling logic.
  • If an upgrade cannot be performed immediately, apply a configuration change or patch that causes the daemon to ignore CC_RESPONSE extensions that arrive without a preceding CC_REQUEST, thereby avoiding state corruption.
  • Continuously monitor Tor logs for repeated crashes or unexpected CC_RESPONSE traffic to confirm that the mitigation is effective.

Generated by OpenCVE AI on September 9, 2026 at 04:28 UTC.

Tracking

Sign in to view the affected projects.

Advisories

No advisories yet.

History

Thu, 10 Sep 2026 21:00:00 +0000

Type Values Removed Values Added
First Time appeared Torproject
Torproject tor
Vendors & Products Torproject
Torproject tor

Wed, 09 Sep 2026 19:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Wed, 09 Sep 2026 04:45:00 +0000

Type Values Removed Values Added
Title Tor Pre‑0.4.9.12 Unchecked CC_RESPONSE Causes Denial of Service

Wed, 09 Sep 2026 01:45:00 +0000

Type Values Removed Values Added
Description Tor before 0.4.9.12 interprets the CC_RESPONSE extension even when CC_REQUEST was not sent, which allows remote attackers to cause a denial of service (crash) because of corrupted congestion-control state. This is TROVE-2026-032.
Weaknesses CWE-669
References
Metrics cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H'}

Subscriptions

Torproject Tor
cve-icon MITRE

Status: PUBLISHED

Assigner: mitre

Published:

Updated: 2026-09-09T18:18:39.270Z

Reserved: 2026-09-09T01:29:45.866Z

Link: CVE-2026-87724

cve-icon Vulnrichment

Updated: 2026-09-09T18:18:32.815Z

cve-icon NVD

Status : Deferred

Published: 2026-09-09T02:16:57.670

Modified: 2026-09-09T19:17:50.287

Link: CVE-2026-87724

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-10T20:45:17Z

Weaknesses
  • CWE-669

    Incorrect Resource Transfer Between Spheres