VulnerabilityPublished 27 Mar 2026

CVE-2026-27859: Open-Xchange OX Dovecot Pro · Uncontrolled Resource Consumption

Affects Open-Xchange OX Dovecot ProSource CVE Database V5

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Not known to be exploited · CVSS 5.3 Medium.

Data as of 29 Oct 2026, 19:04 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 32% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 27 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Open-Xchange GmbHOX Dovecot Pro	Affected <=3.0.2 <=3.1.0 <=2.4.0	Fixed in–

AI-suggested

Use mail transfer agent (MTA) capabilities to limit the number of RFC 2231 MIME parameters in incoming mail messages. Alternatively, upgrade to a fixed version of OX Dovecot Pro that limits processing of these parameters.

Description

CVE-2026-27859 is a medium severity vulnerability in Open-Xchange GmbH's OX Dovecot Pro mail server. It involves uncontrolled resource consumption where a mail message with an excessive number of RFC 2231 MIME parameters causes the LMTP mail delivery process to consume excessive CPU resources. This can degrade mail server performance but does not impact confidentiality or integrity. No public exploits are known. Mitigation involves using MTA capabilities to limit RFC 2231 MIME parameters or upgrading to a fixed version that limits processing. Patch status is not confirmed from the available data.

Impact

The vulnerability causes excessive CPU usage on the mail delivery process, potentially leading to degraded mail server performance or denial of service. There is no impact on confidentiality or integrity of mail data. No public exploits are known, so exploitation is theoretical at this time.

Summary

This vulnerability arises from OX Dovecot Pro's LMTP implementation processing mail messages containing an excessive amount of RFC 2231 MIME parameters, leading to high CPU consumption during mail delivery. The issue results in a denial of service condition by exhausting CPU resources. The CVSS 3.1 base score is 5.3 (medium severity) with network attack vector, low attack complexity, no privileges or user interaction required, and impact limited to availability (no confidentiality or integrity impact). No known exploits exist publicly. Mitigation includes limiting RFC 2231 MIME parameters via MTA or upgrading to a fixed version where processing is constrained.

References

documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0001.json (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 3 Apr 2026, 13:44 UTC

Technical details

References

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