CVE-2026-77587: CWE-911 Improper Update of Reference Count in torproject Tor
Description
Tor versions before 0.4.9.11 contain a use-after-free vulnerability related to improper update of reference counts in conflux objects. This flaw occurs when a recovery leg revives a conflux set whose last linked leg has already been closed, potentially leading to a crash of the client. The vulnerability has a medium severity rating with a CVSS score of 5.9.
CVSS v3.1
Score 5.9medium
Affected software
torproject
Tor
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-77587 describes a use-after-free and potential double free vulnerability in Tor prior to version 0.4.9.11. The issue arises from improper handling of reference counts in conflux objects when a recovery leg revives a conflux set after its last linked leg has been closed. A malicious exit node could exploit this flaw to cause a denial of service by crashing the Tor client.
Potential Impact
The vulnerability can be exploited by a malicious exit node to crash the Tor client, resulting in denial of service. There is no indication of confidentiality or integrity impact. The attack requires network access and has a high attack complexity with no privileges or user interaction needed.
Mitigation Recommendations
A fix is available in Tor version 0.4.9.11. Users should upgrade to version 0.4.9.11 or later to remediate this vulnerability. No other mitigation is indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- mitre
- Date Reserved
- 2026-08-20T20:47:39.624Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6a876922acd9273b491d067b
Added to database: 08/20/2026, 20:52:50 UTC
Last enriched: 09/11/2026, 04:18:05 UTC
Last updated: 10/05/2026, 06:48:18 UTC
Views: 74
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