CVE-2026-27856: dovecot Improper Authentication
Vulnerability summary
CVE-2026-27856 is a high (CVSS 7.4) Improper Authentication vulnerability in dovecot. EPSS estimates a 0.43% chance of exploitation in the next 30 days, higher than 36.2% of scored vulnerabilities.
Advisory lineage
Upstream 0 · Downstream 5 · Related 5Timeline
- 27-03-2026PublishedVulnerability first disclosed.
- 15-07-2026Last modifiedVulnerability information updated.
Description
Doveadm credentials are verified using direct comparison which is susceptible to timing oracle attack. An attacker can use this to determine the configured credentials. Figuring out the credential will lead into full access to the affected component. Limit access to the doveadm http service port, install fixed version. No publicly available exploits are known.
CVSS metrics
5 scores · 5 sources · 1 version- OSV · AlpineEcosystem advisory · calculated5.9MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:NDiffers
- OSV · UbuntuEcosystem advisory · calculated5.9MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:NDiffers
- OSV · DebianEcosystem advisory · calculated5.9MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:NDiffers
- NVDNIST5.9MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:NDiffers
EPSS trend
Probability
0.43%
Chance of exploitation in the next 30 days
Percentile
36%
Versus all other CVEs
30-day change
+0.04 pp
From 0.39% on 20-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-287Improper AuthenticationWhen an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
- CWE-208Observable Timing DiscrepancyTwo separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not.
Affected systems
Alpine1 product
- dovecot≥ 3.0.0, < 2.4.3-r0
Debian1 product
- dovecot< 1:2.3.19.1+dfsg1-2.1+deb12u2 | < 1:2.4.1+dfsg1-6+deb13u4 | < 1:2.4.3+dfsg1-1
Dovecot1 product
- dovecot< 2.4.3
Open-xchange1 product
- dovecot< 2.3.22.1 | ≥ 3.0.0, < 3.0.5 | ≥ 3.1.0, < 3.1.4
Open-xchange gmbh1 product
- ox dovecot pro≤ 2.3.0
Ubuntu1 product
- dovecotAll versions (No fix recorded) | < 1:2.3.16+dfsg1-3ubuntu2.7 | < 1:2.3.21+dfsg1-2ubuntu6.3 | < 1:2.4.1+dfsg1-5ubuntu4.1
6 vendors · 6 products
