CVE-2021-28089 [High] | Denial of Service in Tor

CVE-2021-28089 is rated Moderate Risk (56.2/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.67%). Review affected assets and schedule remediation.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	1.24%	1.67%	+0.43%
2	2026-05-27	1.25%	1.24%	-0.01%
3	2025-12-18	—	1.25%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

1.24%

1.67%

+0.43%

2026-05-27

1.25%

1.24%

-0.01%

2025-12-18

—

1.25%

—

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]

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]

OS Trackers for CVE-2021-28089

vendor	priority	summary	link
`alpine`	high	CVE-2021-28089: 1 source package rows (tor); 13 state rows across 7 repos (3.17-community, 3.18-community, 3.19-community, 3.20-community, 3.21-community, 3.22-community, edge-community); fixed 7, open 6.	https://security.alpinelinux.org/vuln/CVE-2021-28089
`debian`	not yet assigned	CVE-2021-28089 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-2021-28089
`gentoo`	normal	CVE-2021-28089: 1 GLSA(s) (202107-25), 1 atom(s) (net-vpn/tor); latest impact normal.	https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-28089
`ubuntu`	medium	CVE-2021-28089 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-2021-28089

Affected software / configurations for CVE-2021-28089

Vendor	Product	Version	Raw CPE
torproject	tor	< 0.3.5.14	cpe:2.3:a:torproject:tor::::::::
torproject	tor	>= 0.4.4.4, < 0.4.4.8	cpe:2.3:a:torproject:tor::::::::
torproject	tor	>= 0.4.5.0, < 0.4.5.7	cpe:2.3:a:torproject:tor::::::::
torproject	tor	0.4.4.0	cpe:2.3:a:torproject:tor:0.4.4.0:alpha::::::
torproject	tor	0.4.4.1	cpe:2.3:a:torproject:tor:0.4.4.1:alpha::::::
torproject	tor	0.4.4.2	cpe:2.3:a:torproject:tor:0.4.4.2:alpha::::::
torproject	tor	0.4.4.3	cpe:2.3:a:torproject:tor:0.4.4.3:alpha::::::
fedoraproject	fedora	33	cpe:2.3:o:fedoraproject:fedora:33:::::::*

References for CVE-2021-28089

URL	Tags
https://blog.torproject.org/node/2009	Release Notes Vendor Advisory
https://gitlab.torproject.org/tpo/core/tor/-/issues/40304	Vendor Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/HPDXB2GZHG3VNOTWSXQ3QZVHNV76WCU5/
https://security.gentoo.org/glsa/202107-25	Third Party Advisory

URL

CVE-2021-28089

Exploit prediction scoring system (EPSS) score for CVE-2021-28089

Common vulnerability scoring system (CVSS) metrics for CVE-2021-28089

Weakness enumeration for CVE-2021-28089

OS Trackers for CVE-2021-28089

Affected software / configurations for CVE-2021-28089

References for CVE-2021-28089