Quick answers
- Is CVE-2026-77641 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-77641 being exploited in the wild.
- How severe is CVE-2026-77641?
- Medium severity, with a CVSS score of 6.5, published 20 August 2026.
- Which products and versions are affected?
- Tor Project Tor before 0.4.9.9.
- Is there a fix for CVE-2026-77641?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-77641 attacked?
- It is attacked over the network, in a hosted service.
- Am I affected by CVE-2026-77641?
- Check whether you run Torproject Tor. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
The vulnerability is a use-after-free in Tor's conflux (multiplexed circuit) handling. When relay_send_command_from_edge() fails to send a CONFLUX_SWITCH cell, its return value is ignored by the caller. This causes the send failure—which internally calls circuit_mark_for_close() and removes the current leg via cfx_del_leg()—to go undetected. The caller then writes to the now-freed leg structure, resulting in a NULL write and crash. The attack requires network reachability to a Tor relay and can be triggered by sending a malformed CONFLUX_SWITCH cell or inducing a send failure condition.
Affected products
- Tor Project Tor before 0.4.9.9
Timeline
- 2026-08-20: disclosed