Medium

CVE-2026-33603 — Attacker can use a specially crafted base64 exchange between Dovecot and Client to fake…

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.

Published May 12, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: OX

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.2% (30-day exploitation probability)+2
Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.23%

ahead of 13% of scored CVEs · Oct 14, 2026

Affects

Dovecot

Dovecot and 1 more

CVSS base

5.3

Medium · 3 source(s)

Prioritization reference: 6.8 provisional

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

None

none · proof-of-concept · active

Automatable

can an attacker script the kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Dovecot Dovecot, Open-Xchange GmbH Dovecot, Open-Xchange GmbH OX Dovecot Pro).
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Dovecot	Dovecot	< 2.4.4	Vulnerable	NIST National Vulnerability Database
Open-Xchange GmbH	Dovecot	< 3.1.5	Vulnerable	NIST National Vulnerability Database
Open-Xchange GmbH	OX Dovecot Pro	≤ 3.1.0≤ 2.4.0	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Adjacent

Attack complexity

High

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
6.8	CVSS 3.1	Medium	1.6	5.2	security@open-xchange.com via NIST National Vulnerability Database
6.8	CVSS 3.1	Medium	—	—	OX via CVE Program (cve.org) e CISA ADP
5.3	CVSS 3.1	Medium	1.6	3.6	nvd@nist.gov via NIST National Vulnerability Database

CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N (score shown at the top: nvd@nist.gov)

Scoring entities (NIST, CNA, ADP) score independently; each score is shown with its origin. For prioritization we use 6.8 (security@open-xchange.com via NIST National Vulnerability Database) as a conservative provisional reference — not a definitive official score.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-99

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.23%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Not enough vector or weakness data: use the affected application’s logs as a starting point.

application logs

Timeline

What happened to this CVE, newest first.

2026
Affected products added · open-xchange gmbh/ox dovecot pro
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
CVSS changed · 5.3
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
May 12, 2026 · OX

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

1 on the record

documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0002.json
Vendor Advisory, vendor-advisory, NIST National Vulnerability Database

Elsewhere on this site

Dovecot
every CVE for this vendor

CWE-99
other pages naming this weakness

Related CVEs (same products)

Medium CVE-2026-73209 Uncontrolled Recursion in Open-Xchange GmbH OX Dovecot Pro Aug 28, 2026
High CVE-2026-73208 Improper Authentication in Open-Xchange GmbH OX Dovecot Pro Aug 28, 2026
Low CVE-2026-52681 Sieve CPU resource usage is tracked in the compiled script, so an attacker that has… Aug 28, 2026
Medium CVE-2026-52687 Uncontrolled Resource Consumption in Open-Xchange GmbH OX Dovecot Pro Aug 28, 2026
Low CVE-2026-40204 Improper Access Control in Open-Xchange GmbH OX Dovecot Pro Aug 28, 2026
Critical CVE-2026-42007 Use After Free in Open-Xchange GmbH OX Dovecot Pro Aug 28, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-33603 is "Attacker can use a specially crafted base64 exchange between Dovecot and Client to fake…", rated Medium. It affects Dovecot (Dovecot); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.3 describes technical severity. EPSS 0.23% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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