#VU49179 NULL pointer dereference in OpenSMTPD - CVE-2020-35680

Vulnerability identifier: #VU49179

Vulnerability risk: Medium

CVSSv4.0: 4.6 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2020-35680

CWE-ID: CWE-476

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
OpenSMTPD
Server applications / Mail servers

Vendor: OpenBSD

Description

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to a NULL pointer dereference error in smtpd/lka_filter.c in certain configurations. A remote attacker can trigger denial of service conditions 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.

Mitigation
Install update from vendor's website.

Vulnerable software versions

OpenSMTPD: 6.0.0 - 6.7.1p1

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External links
https://github.com/openbsd/src/commit/6c3220444ed06b5796dedfd53a0f4becd903c0d1
https://poolp.org/posts/2020-12-24/december-2020-opensmtpd-6.8.0p1-released-fixed-several-bugs-proposed-several-diffs-book-is-on-github/
https://www.mail-archive.com/misc@opensmtpd.org/msg05188.html

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.