Vulnerability · Published Aug 20, 2026 · Assigned by mitre
CVE-2026-77640
Low 3.7
In plain English
A low-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 32% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
tor before 0.4.9.9 was prone to an infinite loop when decompressing a truncated zlib/gzip stream with done=1. A truncated stream never reaches Z_STREAM_END, causing zlib to return Z_BUF_ERROR with no input remaining, which buf_add_compress() mistook for a full output buffer and retried forever. Fixed by returning TOR_COMPRESS_ERROR in that case so the caller can abort cleanly. This is TROVE-2026-021.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | tor | 0.4.9.9-1 | DEBIAN-CVE-2026-77640 |
| Debian:13 | tor | 0.4.9.11-0+deb13u1 | DEBIAN-CVE-2026-77640 |
| Debian:14 | tor | 0.4.9.9-1 | DEBIAN-CVE-2026-77640 |
| Ubuntu:22.04:LTS | tor | no fix listed | UBUNTU-CVE-2026-77640 |
| Ubuntu:24.04:LTS | tor | no fix listed | UBUNTU-CVE-2026-77640 |
| Ubuntu:26.04:LTS | tor | no fix listed | UBUNTU-CVE-2026-77640 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| torproject | Tor | 0.2.6.1-alpha – before 0.4.9.9 |
Weakness: CWE-1284 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L