CVE-2026-42391

Name	CVE-2026-42391
Description	An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
References	DSA-6526-1
Debian Bugs	1146018

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
dovecot (PTS)	bookworm, bookworm (security)	1:2.3.19.1+dfsg1-2.1+deb12u6	vulnerable
	trixie	1:2.4.1+dfsg1-6+deb13u6	vulnerable
	trixie (security)	1:2.4.1+dfsg1-6+deb13u7	fixed
	forky	1:2.4.5+dfsg1-2	fixed
	sid	1:2.4.5+dfsg1-3	fixed

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
dovecot	source	trixie	1:2.4.1+dfsg1-6+deb13u7		DSA-6526-1
dovecot	source	(unstable)	1:2.4.5+dfsg1-1			1146018

Notes

https://documentation.open-xchange.com/dovecot/security/advisories/html/2026/oxdc-adv-2026-0003.html#cve-2026-42391-imap-pre-login-memory-cpu-growth-with-id-command
Fixed by: https://github.com/dovecot/core/commit/277e5c880a7f6a7741e717036570812910fff7b7
Fixed by: https://github.com/dovecot/core/commit/78518c10c7aa1236c1ed1ebb2d558ce24e6bc122