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Fencer Intel
high 7.5

CVE-2021-34549 json

An issue was discovered in Tor before 0.4.6.5, aka TROVE-2021-005.

published 5y ago modified 4mo ago also EUVD-2021-21201

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.6%
EPSS 1.6% chance of exploitation in 30 days, percentile 76%
public exploits
0
none known

Summary

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.

Patch / fix

  • torproject tor 0.3.5.15, 0.4.4.9, 0.4.5.9, 0.4.6.5
  • tor Debian 14, Debian 13, Debian 12 0.4.5.9-1

debian advisories DEBIAN-CVE-2021-34549

  • tor Ubuntu Pro 16.04 LTS 0.2.9.14-1ubuntu1~16.04.3+esm1
  • tor Ubuntu Pro 18.04 LTS 0.3.2.10-1ubuntu0.2~esm2
  • tor Ubuntu Pro 20.04 LTS 0.4.2.7-1ubuntu0.1~esm1

ubuntu advisories UBUNTU-CVE-2021-34549

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • tor openSUSE Tumbleweed 0.4.6.7-2.2
  • tor Package Hub 15 SP2 0.4.5.9-bp152.2.12.1
  • tor openSUSE Leap 15.2 0.4.5.9-lp152.2.12.1

opensuse advisories openSUSE-SU-2024:11469-1openSUSE-SU-2021:0941-1openSUSE-SU-2021:0926-1

  • tor Alpine 3.12, Alpine 3.11 0.4.4.9-r0

alpine advisories ALPINE-CVE-2021-34549

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • tor Arch Linux 0.4.5.9-1

arch linux advisories AVG-2075

Is CVE-2021-34549 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-34549 updated

tor: hashtable-based CPU denial-of-service attack against relays

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.61% chance of exploitation in the next 30 days, higher than 76% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.