CVE-2026-33603

CVE-2026-33603 is a medium-severity vulnerability in Open-xchange Dovecot with a CVSS 3.x base score of 6.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-99.

Key facts

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.

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.
How severe is CVE-2026-33603?
CVE-2026-33603 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over an adjacent network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-33603 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (13th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33603?
CVE-2026-33603 primarily affects Open-xchange Dovecot. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-33603?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-33603 have an EU (EUVD) identifier?
Yes. CVE-2026-33603 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29468.
When was CVE-2026-33603 published?
CVE-2026-33603 was published on 2026-05-12 and last updated on 2026-06-17.

References

Affected products (2)

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