CVE-2026-77641 Use after free in Tor
A use-after-free vulnerability in Tor allows remote attackers to cause a denial of service via a failed CONFLUX_SWITCH cell transmission.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-77641?
CVE-2026-77641 is a medium-severity use after free vulnerability in torproject Tor, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
tor before 0.4.9.9 was prone to a NULL write after free when sending a CONFLUX_SWITCH cell fails. The return value of relay_send_command_from_edge() was ignored, so a send failure (which calls circuit_mark_for_close() and removes the leg via cfx_del_leg()) would go undetected, causing the caller to write to the now-freed current leg and resulting in a crash. This is TROVE-2026-017.
Weakness: CWE-252
Which versions are affected by CVE-2026-77641?
It affects 1 product.
Products include Torproject Tor.
How do I fix CVE-2026-77641?
Upgrade to a fixed version.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-77641 being exploited?
There is no known exploitation of CVE-2026-77641 in the wild and no public exploit code.
Other vulnerabilities in torproject Tor
Sources
Also known as DEBIAN-CVE-2026-77641, GHSA-r3c6-fj5w-6f75, UBUNTU-CVE-2026-77641.