CVE-2021-34549: Torproject Tor

High severity, CVSS 7.5. EPSS: 1.6% chance of exploitation in the next 30 days.

An issue was discovered in Tor before 0.4.6.5, aka TROVE-2021-005. Hashing is mishandled for certain retrieval of circuit data. Consequently. an attacker can trigger the use of an attacker-chosen circuit ID to cause algorithm inefficiency.

Affected products

• Torproject Tor: before 0.3.5.15 (fixed in 0.3.5.15); from 0.4.0.0, before 0.4.4.9 (fixed in 0.4.4.9); from 0.4.5.0, before 0.4.5.9 (fixed in 0.4.5.9); from 0.4.6.0, before 0.4.6.5 (fixed in 0.4.6.5)

Published 2021-06-29. Last modified 2026-06-17.