CVE-2026-77641: CWE-252 Unchecked Return Value in torproject Tor
Description
A vulnerability in Tor versions before 0.4.9.9 allows a NULL write after free due to unchecked return values when sending a CONFLUX_SWITCH cell fails. This can cause a crash by writing to freed memory.
CVSS v3.1
Score 6.5medium
Affected software
torproject
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
CVE-2026-77641 describes a vulnerability in the Tor software prior to version 0.4.9.9 where the function relay_send_command_from_edge() ignores its return value. If sending a CONFLUX_SWITCH cell fails, the failure triggers circuit_mark_for_close() and removes the leg via cfx_del_leg(). Because the failure is not detected, the caller writes to the now-freed current leg, causing a NULL write after free and resulting in a crash. This is classified under CWE-252 (Unchecked Return Value).
Potential Impact
The vulnerability can cause a denial of service by crashing the Tor process due to a NULL write after free. There is no indication of confidentiality or integrity impact. The CVSS score of 6.5 reflects a medium severity with network attack vector, high attack complexity, no privileges required, no user interaction, unchanged scope, no confidentiality impact, low integrity impact, and high availability impact.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, users should monitor official Tor project communications for updates. No official fix or temporary workaround is currently documented.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- mitre
- Date Reserved
- 2026-08-20T21:09:40.882Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6a87701facd9273b4924712d
Added to database: 08/20/2026, 21:22:39 UTC
Last enriched: 09/10/2026, 13:33:44 UTC
Last updated: 10/05/2026, 06:48:18 UTC
Views: 78
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
External Links
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.