OX Dovecot Pro: Uncontrolled Resource Consumption
CVE-2026-27858 is a high-severity uncontrolled resource consumption vulnerability in OX Dovecot Pro from Open-Xchange, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected OX Dovecot Pro versions: 2.3.0 and earlier; 3.1.0 and earlier; 2.4.0 and earlier. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.82% chance of exploitation within 30 days, higher than 58% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Dovecot to 2.4.3 or a later version.
- Read the advisory on documentation.open-xchange.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by CNA (open-xchange.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.5 | High | CNA (open-xchange.com) |
| CVSS 3.1 | 7.5 | High | CNA |
Official description
Attacker can send a specifically crafted message before authentication that causes managesieve to allocate large amount of memory. Attacker can force managesieve-login to be unavailable by repeatedly crashing the process. Protect access to managesieve protocol, or install fixed version. No publicly available exploits are known.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Uncontrolled Resource Consumption
The product does not properly control the allocation and maintenance of a limited resource.
How developers prevent this class of flaw
- Ensure that protocols have specific limits of scale placed on them.
- Ensure that all failures in resource allocation place the system into a safe posture.
More Uncontrolled Resource Consumption vulnerabilities (CWE-400)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Other references
- access.redhat.com/errata/RHSA-2026:13498
- access.redhat.com/errata/RHSA-2026:13830
- access.redhat.com/errata/RHSA-2026:13857
- access.redhat.com/errata/RHSA-2026:17602
- access.redhat.com/errata/RHSA-2026:17625
- access.redhat.com/errata/RHSA-2026:17626
- access.redhat.com/errata/RHSA-2026:17628
- access.redhat.com/errata/RHSA-2026:17630
- access.redhat.com/errata/RHSA-2026:18053
- access.redhat.com/errata/RHSA-2026:19149
- access.redhat.com/errata/RHSA-2026:19364
- access.redhat.com/errata/RHSA-2026:19453
- access.redhat.com/errata/RHSA-2026:19455
- access.redhat.com/errata/RHSA-2026:26564
- access.redhat.com/security/cve/CVE-2026-27858
Other vulnerabilities in OX Dovecot Pro
- 7.4 High severity
- 7.5 High severity
- 9.1 Critical severity
- 7.5 High severity
- 7.5 High severity
- 9.1 Critical severity
Recent Uncontrolled Resource Consumption vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 8.6 High severity
- 7.5 High severity
- 7.5 High severity
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