CVE-2020-35680 [High] | Denial of Service in Opensmtpd

smtpd/lka_filter.c in OpenSMTPD before 6.8.0p1, in certain configurations, allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a crafted pattern of client activity, because the filter state machine does not properly maintain the I/O channel between the SMTP engine and the filters layer.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	5.80%	3.58%	-2.22%
2	2026-05-29	4.23%	5.80%	+1.57%
3	2025-11-21	—	4.23%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

5.80%

3.58%

-2.22%

2026-05-29

4.23%

5.80%

+1.57%

2025-11-21

—

4.23%

—

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-2020-35680

vendor	priority	summary	link
`alpine`	high	CVE-2020-35680: 1 source package rows (opensmtpd); 6 state rows across 6 repos (3.10-main, 3.11-main, 3.12-main, 3.22-community, edge-community, edge-main); fixed 2, open 4.	https://security.alpinelinux.org/vuln/CVE-2020-35680
`debian`	not yet assigned	CVE-2020-35680 not yet assigned priority: Debian including 1 source packages (opensmtpd), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2020-35680
`gentoo`	low	CVE-2020-35680: 1 GLSA(s) (202105-12), 1 atom(s) (mail-mta/opensmtpd); latest impact low.	https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2020-35680
`ubuntu`	medium	CVE-2020-35680 medium priority: Ubuntu including 1 source packages (opensmtpd), 16 status rows across 16 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): ignored 8, needed 4, needs-triage 2, not-affected 2.	https://ubuntu.com/security/CVE-2020-35680

Affected software / configurations for CVE-2020-35680

Vendor	Product	Version	Raw CPE
opensmtpd	opensmtpd	< 6.8.0	cpe:2.3:a:opensmtpd:opensmtpd::::::::
opensmtpd	opensmtpd	6.8.0	cpe:2.3:a:opensmtpd:opensmtpd:6.8.0:-::::::
opensmtpd	opensmtpd	6.8.0	cpe:2.3:a:opensmtpd:opensmtpd:6.8.0:patch1-rc1::::::
fedoraproject	fedora	32	cpe:2.3:o:fedoraproject:fedora:32:::::::*
fedoraproject	fedora	33	cpe:2.3:o:fedoraproject:fedora:33:::::::*

References for CVE-2020-35680

URL	Tags
https://github.com/openbsd/src/commit/6c3220444ed06b5796dedfd53a0f4becd903c0d1	Patch Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5LKTFBQCHGMVPR4IZWHQIYAPM5J3LN3J/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TYAYXRV2DM5K4RU7RHCDZSA2UF6VCTRC/
https://poolp.org/posts/2020-12-24/december-2020-opensmtpd-6.8.0p1-released-fixed-several-bugs-proposed-several-diffs-book-is-on-github/	Third Party Advisory
https://security.gentoo.org/glsa/202105-12	Third Party Advisory
https://www.mail-archive.com/misc%40opensmtpd.org/msg05188.html

URL

CVE-2020-35680

Exploit prediction scoring system (EPSS) score for CVE-2020-35680

Common vulnerability scoring system (CVSS) metrics for CVE-2020-35680

Weakness enumeration for CVE-2020-35680

OS Trackers for CVE-2020-35680

Affected software / configurations for CVE-2020-35680

References for CVE-2020-35680