# CVE-2026-42391: dovecot: An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, whi...

CVE-2026-42391 is fixed in 12 products on 1 platform, first by RHSA-2026:79371, released August 28, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-42391
- Priority: High
- CVSS: 9.1 (important)
- EPSS: 0.0045
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 28, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | dovecot Debian 12.15 (bookworm) | 1:2.3.19.1+dfsg1-2.1+deb12u7 | [DEBIAN-CVE-2026-42391](https://patchblox.com/security/data/fix/linux/debian-cve-2026-42391.md) | Sep 10, 2026 |
| Linux | dovecot Debian 13.5 (trixie) | 1:2.4.1+dfsg1-6+deb13u7 | [DEBIAN-CVE-2026-42391](https://patchblox.com/security/data/fix/linux/debian-cve-2026-42391.md) | Sep 10, 2026 |
| Linux | dovecot Debian 14 | 1:2.4.5+dfsg1-1 | [DEBIAN-CVE-2026-42391](https://patchblox.com/security/data/fix/linux/debian-cve-2026-42391.md) | Sep 10, 2026 |
| Linux | dovecot RHEL 10 | 2.3.21-19.el10_2.8 | [RHSA-2026:79371](https://patchblox.com/security/data/fix/linux/rhsa-2026-79371.md) | Aug 28, 2026 |
| Linux | dovecot RHEL 8 | 1:2.3.16-16.el8_10 | [RHSA-2026:76763](https://patchblox.com/security/data/fix/linux/rhsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot RHEL 9 | 1:2.3.16-18.el9_8.8 | [RHSA-2026:80825](https://patchblox.com/security/data/fix/linux/rhsa-2026-80825.md) | Oct 13, 2026 |
| Linux | dovecot almalinux 10 | 1:2.3.21-19.el10_2.8 | [ALSA-2026:79371](https://patchblox.com/security/data/fix/linux/alsa-2026-79371.md) | Oct 8, 2026 |
| Linux | dovecot almalinux 8 | 1:2.3.16-16.el8_10 | [ALSA-2026:76763](https://patchblox.com/security/data/fix/linux/alsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot almalinux 9 | 1:2.3.16-18.el9_8.8 | [ALSA-2026:80825](https://patchblox.com/security/data/fix/linux/alsa-2026-80825.md) | Nov 7, 2026 |
| Linux | dovecot amzn 2023 | 1:2.3.20-1.amzn2023.0.4 | [ALAS2023-2026-3109](https://patchblox.com/security/data/fix/linux/alas2023-2026-3109.md) | Sep 28, 2026 |
| Linux | dovecot ol 10 | 1:2.3.21-19.el10_2.8 | [ELSA-2026-79371](https://patchblox.com/security/data/fix/linux/elsa-2026-79371.md) | Oct 8, 2026 |
| Linux | dovecot ol 8 | 1:2.3.16-16.el8_10 | [ELSA-2026-76763](https://patchblox.com/security/data/fix/linux/elsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot ol 9 | 1:2.3.16-18.el9_8.8 | [ELSA-2026-80825](https://patchblox.com/security/data/fix/linux/elsa-2026-80825.md) | Nov 7, 2026 |
| Linux | dovecot rocky 10 | 1:2.3.21-19.el10_2.8 | [RLSA-2026:79371](https://patchblox.com/security/data/fix/linux/rlsa-2026-79371.md) | Nov 7, 2026 |
| Linux | dovecot rocky 8 | 1:2.3.16-16.el8_10 | [RLSA-2026:76763](https://patchblox.com/security/data/fix/linux/rlsa-2026-76763.md) | Oct 7, 2026 |
| Linux | dovecot rocky 9 | 1:2.3.16-18.el9_8.8 | [RLSA-2026:80825](https://patchblox.com/security/data/fix/linux/rlsa-2026-80825.md) | Nov 7, 2026 |
| Linux | dovecot-debuginfo amzn 2023 | 1:2.3.20-1.amzn2023.0.4 | [ALAS2023-2026-3109](https://patchblox.com/security/data/fix/linux/alas2023-2026-3109.md) | Sep 28, 2026 |
| Linux | dovecot-debugsource amzn 2023 | 1:2.3.20-1.amzn2023.0.4 | [ALAS2023-2026-3109](https://patchblox.com/security/data/fix/linux/alas2023-2026-3109.md) | Sep 28, 2026 |
| Linux | dovecot-devel RHEL 8 | 1:2.3.16-16.el8_10 | [RHSA-2026:76763](https://patchblox.com/security/data/fix/linux/rhsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot-devel RHEL 9 | 1:2.3.16-18.el9_8.8 | [RHSA-2026:80825](https://patchblox.com/security/data/fix/linux/rhsa-2026-80825.md) | Oct 13, 2026 |
| Linux | dovecot-devel almalinux 10 | 1:2.3.21-19.el10_2.8 | [ALSA-2026:79371](https://patchblox.com/security/data/fix/linux/alsa-2026-79371.md) | Oct 8, 2026 |
| Linux | dovecot-devel almalinux 8 | 1:2.3.16-16.el8_10 | [ALSA-2026:76763](https://patchblox.com/security/data/fix/linux/alsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot-devel almalinux 9 | 1:2.3.16-18.el9_8.8 | [ALSA-2026:80825](https://patchblox.com/security/data/fix/linux/alsa-2026-80825.md) | Nov 7, 2026 |
| Linux | dovecot-devel amzn 2023 | 1:2.3.20-1.amzn2023.0.4 | [ALAS2023-2026-3109](https://patchblox.com/security/data/fix/linux/alas2023-2026-3109.md) | Sep 28, 2026 |
| Linux | dovecot-devel ol 10 | 1:2.3.21-19.el10_2.8 | [ELSA-2026-79371](https://patchblox.com/security/data/fix/linux/elsa-2026-79371.md) | Oct 8, 2026 |
| Linux | dovecot-devel ol 8 | 1:2.3.16-16.el8_10 | [ELSA-2026-76763](https://patchblox.com/security/data/fix/linux/elsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot-devel ol 9 | 1:2.3.16-18.el9_8.8 | [ELSA-2026-80825](https://patchblox.com/security/data/fix/linux/elsa-2026-80825.md) | Nov 7, 2026 |
| Linux | dovecot-mysql RHEL 8 | 1:2.3.16-16.el8_10 | [RHSA-2026:76763](https://patchblox.com/security/data/fix/linux/rhsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot-mysql RHEL 9 | 1:2.3.16-18.el9_8.8 | [RHSA-2026:80825](https://patchblox.com/security/data/fix/linux/rhsa-2026-80825.md) | Oct 13, 2026 |
| Linux | dovecot-mysql almalinux 10 | 1:2.3.21-19.el10_2.8 | [ALSA-2026:79371](https://patchblox.com/security/data/fix/linux/alsa-2026-79371.md) | Oct 8, 2026 |
| Linux | dovecot-mysql almalinux 8 | 1:2.3.16-16.el8_10 | [ALSA-2026:76763](https://patchblox.com/security/data/fix/linux/alsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot-mysql almalinux 9 | 1:2.3.16-18.el9_8.8 | [ALSA-2026:80825](https://patchblox.com/security/data/fix/linux/alsa-2026-80825.md) | Nov 7, 2026 |
| Linux | dovecot-mysql amzn 2023 | 1:2.3.20-1.amzn2023.0.4 | [ALAS2023-2026-3109](https://patchblox.com/security/data/fix/linux/alas2023-2026-3109.md) | Sep 28, 2026 |
| Linux | dovecot-mysql ol 10 | 1:2.3.21-19.el10_2.8 | [ELSA-2026-79371](https://patchblox.com/security/data/fix/linux/elsa-2026-79371.md) | Oct 8, 2026 |
| Linux | dovecot-mysql ol 8 | 1:2.3.16-16.el8_10 | [ELSA-2026-76763](https://patchblox.com/security/data/fix/linux/elsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot-mysql ol 9 | 1:2.3.16-18.el9_8.8 | [ELSA-2026-80825](https://patchblox.com/security/data/fix/linux/elsa-2026-80825.md) | Nov 7, 2026 |
| Linux | dovecot-mysql-debuginfo amzn 2023 | 1:2.3.20-1.amzn2023.0.4 | [ALAS2023-2026-3109](https://patchblox.com/security/data/fix/linux/alas2023-2026-3109.md) | Sep 28, 2026 |
| Linux | dovecot-pgsql RHEL 8 | 1:2.3.16-16.el8_10 | [RHSA-2026:76763](https://patchblox.com/security/data/fix/linux/rhsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot-pgsql RHEL 9 | 1:2.3.16-18.el9_8.8 | [RHSA-2026:80825](https://patchblox.com/security/data/fix/linux/rhsa-2026-80825.md) | Oct 13, 2026 |
| Linux | dovecot-pgsql almalinux 10 | 1:2.3.21-19.el10_2.8 | [ALSA-2026:79371](https://patchblox.com/security/data/fix/linux/alsa-2026-79371.md) | Oct 8, 2026 |
| Linux | dovecot-pgsql almalinux 8 | 1:2.3.16-16.el8_10 | [ALSA-2026:76763](https://patchblox.com/security/data/fix/linux/alsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot-pgsql almalinux 9 | 1:2.3.16-18.el9_8.8 | [ALSA-2026:80825](https://patchblox.com/security/data/fix/linux/alsa-2026-80825.md) | Nov 7, 2026 |
| Linux | dovecot-pgsql amzn 2023 | 1:2.3.20-1.amzn2023.0.4 | [ALAS2023-2026-3109](https://patchblox.com/security/data/fix/linux/alas2023-2026-3109.md) | Sep 28, 2026 |
| Linux | dovecot-pgsql ol 10 | 1:2.3.21-19.el10_2.8 | [ELSA-2026-79371](https://patchblox.com/security/data/fix/linux/elsa-2026-79371.md) | Oct 8, 2026 |
| Linux | dovecot-pgsql ol 8 | 1:2.3.16-16.el8_10 | [ELSA-2026-76763](https://patchblox.com/security/data/fix/linux/elsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot-pgsql ol 9 | 1:2.3.16-18.el9_8.8 | [ELSA-2026-80825](https://patchblox.com/security/data/fix/linux/elsa-2026-80825.md) | Nov 7, 2026 |
| Linux | dovecot-pgsql-debuginfo amzn 2023 | 1:2.3.20-1.amzn2023.0.4 | [ALAS2023-2026-3109](https://patchblox.com/security/data/fix/linux/alas2023-2026-3109.md) | Sep 28, 2026 |
| Linux | dovecot-pigeonhole RHEL 8 | 1:2.3.16-16.el8_10 | [RHSA-2026:76763](https://patchblox.com/security/data/fix/linux/rhsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot-pigeonhole RHEL 9 | 1:2.3.16-18.el9_8.8 | [RHSA-2026:80825](https://patchblox.com/security/data/fix/linux/rhsa-2026-80825.md) | Oct 13, 2026 |
| Linux | dovecot-pigeonhole almalinux 10 | 1:2.3.21-19.el10_2.8 | [ALSA-2026:79371](https://patchblox.com/security/data/fix/linux/alsa-2026-79371.md) | Oct 8, 2026 |
| Linux | dovecot-pigeonhole almalinux 8 | 1:2.3.16-16.el8_10 | [ALSA-2026:76763](https://patchblox.com/security/data/fix/linux/alsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot-pigeonhole almalinux 9 | 1:2.3.16-18.el9_8.8 | [ALSA-2026:80825](https://patchblox.com/security/data/fix/linux/alsa-2026-80825.md) | Nov 7, 2026 |
| Linux | dovecot-pigeonhole amzn 2023 | 1:2.3.20-1.amzn2023.0.4 | [ALAS2023-2026-3109](https://patchblox.com/security/data/fix/linux/alas2023-2026-3109.md) | Sep 28, 2026 |
| Linux | dovecot-pigeonhole ol 10 | 1:2.3.21-19.el10_2.8 | [ELSA-2026-79371](https://patchblox.com/security/data/fix/linux/elsa-2026-79371.md) | Oct 8, 2026 |
| Linux | dovecot-pigeonhole ol 8 | 1:2.3.16-16.el8_10 | [ELSA-2026-76763](https://patchblox.com/security/data/fix/linux/elsa-2026-76763.md) | Oct 6, 2026 |
| Linux | dovecot-pigeonhole ol 9 | 1:2.3.16-18.el9_8.8 | [ELSA-2026-80825](https://patchblox.com/security/data/fix/linux/elsa-2026-80825.md) | Nov 7, 2026 |
| Linux | dovecot-pigeonhole-debuginfo amzn 2023 | 1:2.3.20-1.amzn2023.0.4 | [ALAS2023-2026-3109](https://patchblox.com/security/data/fix/linux/alas2023-2026-3109.md) | Sep 28, 2026 |
| Linux | dovecot23 sles 15.6 | 2.3.21.1-150200.76.1 | [SUSE-SU-2026:4139-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-4139-1.md) | Sep 14, 2026 |
| Linux | dovecot23 sles 15.7 | 2.3.21.1-150200.76.1 | [SUSE-SU-2026:4139-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-4139-1.md) | Sep 14, 2026 |
| Linux | dovecot24 opensuse-leap 16.0 | 2.4.4-160000.2.1 | [OPENSUSE-SU-2026:21720-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21720-1.md) | Sep 1, 2026 |
| Linux | dovecot24 sles 16.0 | 2.4.4-160000.2.1 | [SUSE-SU-2026:23595-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23595-1.md) | Sep 1, 2026 |

---

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