CVE-2021-34549

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-06-29 · updated 2026-06-17
Weakness: CWE-400

Description

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; from 0.4.0.0 before 0.4.4.9; from 0.4.5.0 before 0.4.5.9; from 0.4.6.0 before 0.4.6.5 — fixed in 0.3.5.15, 0.4.4.9, 0.4.5.9, 0.4.6.5

How to fix

Upgrade to a fixed version: torproject Tor 0.3.5.15, 0.4.4.9, 0.4.5.9, 0.4.6.5. Check the vendor advisory for mitigations.

References

https://blog.torproject.org/node/2041
https://gitlab.torproject.org/tpo/core/tor/-/issues/40391
https://security.gentoo.org/glsa/202107-25
https://blog.torproject.org/node/2041
https://gitlab.torproject.org/tpo/core/tor/-/issues/40391
https://security.gentoo.org/glsa/202107-25

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