CVE-2026-87724: CWE-669 Incorrect Resource Transfer Between Spheres in torprject Tor
Description
CVE-2026-87724 is a medium severity vulnerability in Tor before version 0.4.9.12. It allows remote attackers to cause a denial of service by triggering a crash. The issue arises because Tor processes the CC_RESPONSE extension even when the CC_REQUEST extension was not sent, which corrupts the congestion-control state and leads to a crash.
CVSS v3.1
Score 6.5medium
Affected software
torprject
Tor
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
This vulnerability in Tor versions >=0.4.9.3-alpha and <0.4.9.12 involves improper handling of congestion control extensions. Specifically, Tor interprets the CC_RESPONSE extension without a preceding CC_REQUEST extension, causing corruption of the congestion-control state and resulting in a denial of service via crash. The CVSS v3.1 score is 6.5, reflecting a network attack vector with high attack complexity, no privileges required, no user interaction, unchanged scope, no confidentiality impact, limited integrity impact, and high availability impact.
Potential Impact
Remote attackers can cause a denial of service by crashing the Tor process, disrupting service availability. There is no impact on confidentiality or significant integrity loss according to the CVSS vector. No known exploits are reported in the wild.
Mitigation Recommendations
A fix is available in Tor version 0.4.9.12. Users should upgrade to version 0.4.9.12 or later to remediate this vulnerability. No other mitigation steps are indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- mitre
- Date Reserved
- 2026-09-09T01:29:45.866Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6aa0b867acd9273b4989b578
Added to database: 09/09/2026, 01:37:43 UTC
Last enriched: 10/17/2026, 23:22:43 UTC
Last updated: 10/23/2026, 15:10:15 UTC
Views: 79
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