Medium severity · published May 12, 2026
CVE-2026-33603
Attacker can use a specially crafted base64 exchange between Dovecot and Client to fake SCRAM TLS channel binding
5.3
CVSS
0.2%
EPSS
No
On KEV
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 vector
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Attack vector
Adjacent
Complexity
High
Privileges
None
User interaction
None
Confidentiality
High
Integrity
None
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 12% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
OD
OX Dovecot Pro · Open-Xchange GmbH
through 3.1.0; through 2.4.0 · source: vendor
DO
Dovecot · Dovecot
before 2.4.4 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-33603
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-33603
Vendor Advisory
https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0002.json
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