No exploitation reportedFix available

CVE-2021-34549

Q: Is CVE-2021-34549 actively exploited?

Active exploitation of CVE-2021-34549 has not been confirmed. Its EPSS score was 1.6% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-34549?

CVE-2021-34549 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

No exploitation reported by the sources we read.

Published2021-06-29
Fixed in0.4.6.5 · 0.4.5.9 · 0.4.4.9 · 0.3.5.15
WeaknessCWE-400

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC

2021-06-2912:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-34549?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-34549?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Torproject tor

Branch	Affected	Fixed in	Source
0.4	≥ 0.4.6.0, < 0.4.6.5	0.4.6.5	NVD
0.4	≥ 0.4.5.0, < 0.4.5.9	0.4.5.9	NVD
0.4	≥ 0.4.0.0, < 0.4.4.9	0.4.4.9	NVD
0.3	< 0.3.5.15	0.3.5.15	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Update Torproject tor to 0.4.6.5 · 0.4.5.9 · 0.4.4.9 · 0.3.5.15

Advisories and patches

blog.torproject.orgRelease Notes · Vendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

NVDCVSS 3.17.5read 2026-10-23
NVDCVSS 2.05read 2026-10-23
NVDweakness (CWE)CWE-400read 2026-10-23
FIRST EPSSEPSS score1.6 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: 2021-06-29
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-34549?

Is CVE-2021-34549 actively exploited?

Active exploitation of CVE-2021-34549 has not been confirmed. Its EPSS score was 1.6% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-34549?

CVE-2021-34549 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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