CVE-2026-77584 Use after free in Tor

High 7.0 Published 20 Aug 2026 Updated 25 Aug 2026

A malicious client can trigger a use-after-free in Tor by sending specific relay commands, potentially leading to code execution or denial of service.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-77584?

CVE-2026-77584 is a high-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 0.4.9.10 did not reject a CONFLUX_LINK cell that arrives on a circuit which already has attached streams. A malicious client could send a RELAY_COMMAND_BEGIN before the CONFLUX_LINK on the same circuit, attaching an exit stream that would later end up orphan leaving a dangling circuit back-pointer and a use-after-free (UAF) when the circuit is freed. This is TROVE-2026-025.

Weakness: CWE-821

Which versions are affected by CVE-2026-77584?

It affects 1 product.

Products include Torproject Tor.

How do I fix CVE-2026-77584?

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-2026-77584 being exploited?

There is no known exploitation of CVE-2026-77584 in the wild and no public exploit code.

Sources

Also known as DEBIAN-CVE-2026-77584, GHSA-j5c4-cwjr-6vv5, UBUNTU-CVE-2026-77584.