CVE-2026-33603

Description

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.

CVSS v3.1 Score

6.8

MEDIUM

CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS — Exploit Prediction

0.0001

Probability of exploitation

0.01%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-99 CWE-99

Affected Products

Vendor	Product	Versions
dovecot	dovecot	< 2.4.4
open-xchange	dovecot	< 3.1.5

References

Advisories & Patches

https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0002.json

Frequently Asked Questions

What is CVE-2026-33603? +

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. It has a CVSS v3.1 base score of 6.8 (MEDIUM).

How severe is CVE-2026-33603? +

CVE-2026-33603 has a CVSS v3.1 score of 6.8 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0001, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-33603? +

CVE-2026-33603 affects products from dovecot, open-xchange, specifically: dovecot. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-33603? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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