CVE-2021-34549

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.

Published: 2021-06-29 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-34549 is rated Moderate Risk (56.4/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.61%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-34549

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.65% 1.61% +0.96%
2 2025-03-30 1.34% 0.65% -0.70%
3 2025-03-29 — 1.34% —

Full EPSS history (10 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-34549

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-34549

OS Trackers for CVE-2021-34549

vendor priority summary link
alpine high CVE-2021-34549: 1 source package rows (tor); 10 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 10. https://security.alpinelinux.org/vuln/CVE-2021-34549
debian not yet assigned CVE-2021-34549 not yet assigned priority: Debian including 1 source packages (tor), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-34549
gentoo normal CVE-2021-34549: 1 GLSA(s) (202107-25), 1 atom(s) (net-vpn/tor); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-34549
ubuntu medium CVE-2021-34549 medium priority: Ubuntu including 1 source packages (tor), 15 status rows across 15 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, trusty, upstream, xenial): not-affected 8, released 4, ignored 3. https://ubuntu.com/security/CVE-2021-34549

Affected software / configurations for CVE-2021-34549

Vendor Product Version Raw CPE
torproject tor < 0.3.5.15 cpe:2.3:a:torproject:tor:*:*:*:*:*:*:*:*
torproject tor >= 0.4.0.0, < 0.4.4.9 cpe:2.3:a:torproject:tor:*:*:*:*:*:*:*:*
torproject tor >= 0.4.5.0, < 0.4.5.9 cpe:2.3:a:torproject:tor:*:*:*:*:*:*:*:*
torproject tor >= 0.4.6.0, < 0.4.6.5 cpe:2.3:a:torproject:tor:*:*:*:*:*:*:*:*

References for CVE-2021-34549

cvelogic Threat Intelligence