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Fencer Vulns
medium 6.8

CVE-2026-33603 json

Attacker can use a specially crafted base64 exchange between Dovecot and Client to fake SCRAM TLS channel binding.

published 2026-05-12 5 mo ago modified 2026-10-26 13 d ago also EUVD-2026-29468

cvss
6.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 11%
public exploits
0
none known

Summary

Attacker can use a specially crafted base64 exchange between Dovecot and Client to fake SCRAM TLS channel binding. This requires that the attacker is able to position itself between Dovecot and the client connection. If successful, the attacker can eavesdrop communications between Dovecot and client as MITM proxy. Install fixed version. No publicly available exploits are known.

Patch / fix

  • dovecot dovecot 2.4.4, 3.1.5
  • open-xchange dovecot 2.4.4, 3.1.5
  • dovecot Debian 12 1:2.3.19.1+dfsg1-2.1+deb12u6
  • dovecot Debian 13 1:2.4.1+dfsg1-6+deb13u6
  • dovecot Debian 14 1:2.4.4+dfsg1-1

debian advisories DEBIAN-CVE-2026-33603

  • dovecot Ubuntu 22.04 LTS 1:2.3.16+dfsg1-3ubuntu2.9
  • dovecot Ubuntu 24.04 LTS 1:2.3.21+dfsg1-2ubuntu6.5
  • dovecot Ubuntu 25.10 1:2.4.1+dfsg1-5ubuntu4.2
  • dovecot Ubuntu 26.04 LTS 1:2.4.2+dfsg1-3ubuntu2.1

ubuntu advisories UBUNTU-CVE-2026-33603

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • 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 2.4.4-160000.1.1
  • dovecot22 SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 2.2.31-19.37.2

suse advisories SUSE-SU-2026:4139-1SUSE-SU-2026:2645-1SUSE-SU-2026:22185-1

  • dovecot24 openSUSE Leap 16.0 2.4.4-160000.1.1
  • dovecot24 openSUSE Tumbleweed 2.4.4-1.1

opensuse advisories openSUSE-SU-2026:21109-1openSUSE-SU-2026:10766-1

  • dovecot Alpine 3.24, Alpine 3.23 2.4.4-r0

alpine advisories ALPINE-CVE-2026-33603

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-2026-33603 updated cvss 6.8

dovecot: Dovecot: Information disclosure via SCRAM TLS channel binding bypass

  • Red Hat Enterprise Linux 6 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
total
Assessed
5 mo ago

Exploit prediction

0.21% chance of exploitation in the next 30 days, higher than 11% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.8 CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD 3.1 5.3 CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected products

  • Open-Xchange GmbH OX Dovecot Pro

Classification

Weakness
  • CWE-99 Improper Control of Resource Identifiers

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.