What’s Vulnerable › Vulnerabilities
CVE-2026-77640
- Severity: medium (CVSS 5.3 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.4% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-08-20 · updated 2026-10-18
- Weakness: CWE-1284
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 products
- torproject Tor: before 0.4.9.9 — fixed in 0.4.9.9
How to fix
Upgrade to a fixed version: torproject Tor 0.4.9.9. Check the vendor advisory for mitigations.
References
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