CVE-2026-77639 Denial of service in Tor
Attackers can bypass compression bomb detection in Tor by concatenating sub-streams, causing resource exhaustion and 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-2026-77639?
CVE-2026-77639 is a medium-severity denial of service 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 compression bomb bypass where an attacker could concatenate many gzip or zlib sub-streams, each just under the per-stream detection threshold, to avoid the compression bomb check entirely. This is TROVE-2026-022.
Weakness: CWE-420
Which versions are affected by CVE-2026-77639?
It affects 1 product.
Products include Torproject Tor.
How do I fix CVE-2026-77639?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-77639 being exploited?
There is no known exploitation of CVE-2026-77639 in the wild and no public exploit code.
Other vulnerabilities in torproject Tor
Sources
Also known as DEBIAN-CVE-2026-77639, GHSA-jm5p-g55h-rwhg, UBUNTU-CVE-2026-77639.