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Fencer Vulns
low 3.7

CVE-2026-40203 json

When IMAP compression is enabled, the same compression state is reused across responses in a session, so response sizes depend on both atta…

published 2026-08-28 2 mo ago modified 2026-09-03 2 mo ago also EUVD-2026-67669

cvss
3.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 17%
public exploits
0
none known

Summary

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.

Patch / fix

  • Open-Xchange GmbH OX Dovecot Pro 2.3.22.2, 3.0.7, 3.1.6
  • Open-Xchange GmbH OX Dovecot CE 2.4.5
  • dovecot Debian 12 1:2.3.19.1+dfsg1-2.1+deb12u7
  • dovecot Debian 13 1:2.4.1+dfsg1-6+deb13u7
  • dovecot Debian 14 1:2.4.5+dfsg1-1

debian advisories DEBIAN-CVE-2026-40203

  • dovecot23 SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 2.3.21.1-150200.76.1
  • dovecot24 SLES for SAP applications 16.0, SLES 16.0 2.4.4-160000.2.1
  • dovecot22 SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 2.2.31-19.40.1

suse advisories SUSE-SU-2026:4139-1SUSE-SU-2026:3919-1SUSE-SU-2026:23595-1

  • dovecot24 openSUSE Leap 16.0 2.4.4-160000.2.1
  • dovecot24 openSUSE Tumbleweed 2.4.5-1.1

opensuse advisories openSUSE-SU-2026:21720-1openSUSE-SU-2026:11629-1

  • dovecot Alpine 3.24, Alpine 3.23 2.4.5-r0

alpine advisories ALPINE-CVE-2026-40203

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-40203 updated cvss 3.7

dovecot: Dovecot: Information disclosure via IMAP compression side-channel

  • Red Hat Enterprise Linux 6 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole Red Hat Enterprise Linux 8 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole Red Hat Enterprise Linux 9 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole Red Hat Enterprise Linux 10 dovecot
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.26% chance of exploitation in the next 30 days, higher than 17% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Affected products

  • Open-Xchange GmbH OX Dovecot Pro
  • Open-Xchange GmbH OX Dovecot CE

Classification

Weakness
  • CWE-200 Exposure of Sensitive Information to an Unauthorized Actor

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.