Vulnerability · Published Aug 20, 2026 · Assigned by mitre
CVE-2026-77639
Medium 5.3
In plain English
A medium-severity security flaw in Tor from torproject. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 33% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)5.3Medium
Exploit odds (30 days)0.4%top 66.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | tor | 0.4.9.9-1 | DEBIAN-CVE-2026-77639 |
| Debian:13 | tor | 0.4.9.11-0+deb13u1 | DEBIAN-CVE-2026-77639 |
| Debian:14 | tor | 0.4.9.9-1 | DEBIAN-CVE-2026-77639 |
| Ubuntu:22.04:LTS | tor | no fix listed | UBUNTU-CVE-2026-77639 |
| Ubuntu:24.04:LTS | tor | no fix listed | UBUNTU-CVE-2026-77639 |
| Ubuntu:26.04:LTS | tor | no fix listed | UBUNTU-CVE-2026-77639 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| torproject | Tor | 0.3.1.1-alpha – before 0.4.9.9 |
Weakness: CWE-420 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L