# CVE-2026-40203: dovecot: When IMAP compression is enabled, the same compression state is reused across responses in a session, so response siz...

CVE-2026-40203 is fixed in 12 products on 1 platform, first by SUSE-SU-2026:23595-1, released September 1, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-40203
- Priority: Routine
- CVSS: 3.7 (low)
- EPSS: 0.0026
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 28, 2026

## Description

When IMAP compression is enabled, the same compression state is reused across responses in a session, so response sizes depend on both attacker-supplied mail and other mail in the same mailbox. An attacker that can send mail to a user and can also observe the sizes of that user's IMAP traffic can confirm whether the body of a small message matches a guessed text. Recovery of arbitrary unknown content was not demonstrated, but the attack can disclose whether a secret-like message body matches a candidate. Disable IMAP compression. 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-2026-40203](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40203.md) | Sep 10, 2026 |
| Linux | dovecot Debian 13.5 (trixie) | 1:2.4.1+dfsg1-6+deb13u7 | [DEBIAN-CVE-2026-40203](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40203.md) | Sep 10, 2026 |
| Linux | dovecot Debian 14 | 1:2.4.5+dfsg1-1 | [DEBIAN-CVE-2026-40203](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40203.md) | Sep 10, 2026 |
| Linux | dovecot Fedora 43 | 1:2.4.5-1.fc43 | [FEDORA-2026-E8A6485109](https://patchblox.com/security/data/fix/linux/fedora-2026-e8a6485109.md) | Sep 10, 2026 |
| Linux | dovecot-debuginfo Fedora 43 | 1:2.4.5-1.fc43 | [FEDORA-2026-E8A6485109](https://patchblox.com/security/data/fix/linux/fedora-2026-e8a6485109.md) | Sep 10, 2026 |
| Linux | dovecot-debugsource Fedora 43 | 1:2.4.5-1.fc43 | [FEDORA-2026-E8A6485109](https://patchblox.com/security/data/fix/linux/fedora-2026-e8a6485109.md) | Sep 10, 2026 |
| Linux | dovecot-devel Fedora 43 | 1:2.4.5-1.fc43 | [FEDORA-2026-E8A6485109](https://patchblox.com/security/data/fix/linux/fedora-2026-e8a6485109.md) | Sep 10, 2026 |
| Linux | dovecot-mysql Fedora 43 | 1:2.4.5-1.fc43 | [FEDORA-2026-E8A6485109](https://patchblox.com/security/data/fix/linux/fedora-2026-e8a6485109.md) | Sep 10, 2026 |
| Linux | dovecot-mysql-debuginfo Fedora 43 | 1:2.4.5-1.fc43 | [FEDORA-2026-E8A6485109](https://patchblox.com/security/data/fix/linux/fedora-2026-e8a6485109.md) | Sep 10, 2026 |
| Linux | dovecot-pgsql Fedora 43 | 1:2.4.5-1.fc43 | [FEDORA-2026-E8A6485109](https://patchblox.com/security/data/fix/linux/fedora-2026-e8a6485109.md) | Sep 10, 2026 |
| Linux | dovecot-pgsql-debuginfo Fedora 43 | 1:2.4.5-1.fc43 | [FEDORA-2026-E8A6485109](https://patchblox.com/security/data/fix/linux/fedora-2026-e8a6485109.md) | Sep 10, 2026 |
| Linux | dovecot-pigeonhole Fedora 43 | 1:2.4.5-1.fc43 | [FEDORA-2026-E8A6485109](https://patchblox.com/security/data/fix/linux/fedora-2026-e8a6485109.md) | Sep 10, 2026 |
| Linux | dovecot-pigeonhole-debuginfo Fedora 43 | 1:2.4.5-1.fc43 | [FEDORA-2026-E8A6485109](https://patchblox.com/security/data/fix/linux/fedora-2026-e8a6485109.md) | Sep 10, 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 |

---

Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.