What is CVE-2021-34548?

CVE-2021-34548 is a high-severity vulnerability in Torproject Tor, classified under Authentication Bypass by Spoofing. CVSS score: 7.5/10. Published 2021-06-29.

How severe is CVE-2021-34548?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Torproject Tor

CVE-2021-34548

An issue was discovered in Tor before 0.4.6.5, aka TROVE-2021-003. An attacker can forge RELAY_END or RELAY_RESOLVED to bypass the intended access control for ending a stream.

Published 2021-06-29 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.027 (85.5th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 85th percentile — 85.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.027 · newest: 0.027 · change: 0.000

Affected products

Torproject Tor

Weakness classification (CWE)

CWE-290 — Authentication Bypass by Spoofing

References

gitlab.torproject.org/tpo/core/tor/-/issues/40389 (Broken Link)
blog.torproject.org/node/2041 (Release Notes, Vendor Advisory)
security.gentoo.org/glsa/202107-25 (vendor-advisory, Third Party Advisory)
packetstormsecurity.com/files/163510/Tor-Half-Closed-Connection-Stream-Confusio… (VDB Entry, Third Party Advisory)

Frequently asked questions

What is CVE-2021-34548?: CVE-2021-34548 is a high-severity vulnerability in Torproject Tor, classified under Authentication Bypass by Spoofing. CVSS score: 7.5/10. Published 2021-06-29.
How severe is CVE-2021-34548?: High severity. CVSS v3 base score is 7.5 out of 10.