How severe is CVE-2026-27858?

CVE-2026-27858 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-27858 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (52nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-27858?

CVE-2026-27858 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-2026-27858?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-27858 have an EU (EUVD) identifier?

Yes. CVE-2026-27858 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16569.

When was CVE-2026-27858 published?

CVE-2026-27858 was published on 2026-03-27 and last updated on 2026-06-30.

CVE-2026-27858

CVE-2026-27858 is a high-severity vulnerability in Open-xchange Dovecot with a CVSS 3.x base score of 7.5. 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-400.

Key facts

Severity: High (CVSS 3.x base score 7.5)
EPSS exploit prediction: 1% (52nd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-16569
Weakness: CWE-400
Affected product: Open-xchange Dovecot
Published: 2026-03-27
Last modified: 2026-06-30

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.

Frequently asked questions

What is CVE-2026-27858?: 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.
How severe is CVE-2026-27858?: CVE-2026-27858 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-27858 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (52nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-27858?: CVE-2026-27858 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-2026-27858?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-27858 have an EU (EUVD) identifier?: Yes. CVE-2026-27858 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16569.
When was CVE-2026-27858 published?: CVE-2026-27858 was published on 2026-03-27 and last updated on 2026-06-30.

References

Affected products (2)

cpe:2.3:a:dovecot:dovecot:*:*:*:*:*:*:*:*
cpe:2.3:a:open-xchange:dovecot:*:*:*:*:pro:*:*:*

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