VulnerabilityPublished 27 Mar 2026Updated 4 May 2026

CVE-2026-27860: If auth_username_chars is empty, it is possible to inject arbitrary LDAP filter to Dovecot's LDAP

Affects dovecotSource GCVE Database

Authoritative record:CVE-2026-27860· Low 3.7

Not known to be exploited · CVSS 3.7 Low : upgrade to 1:2.4.1+dfsg1-5ubuntu4.1 when convenient.

Data as of 27 Oct 2026, 01:13 UTC

CVSS 3.1 base score

3.7Low

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

Patch: Available – fixed in 1:2.4.1+dfsg1-5ubuntu4.1

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

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

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: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
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: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within 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
Weaponised: 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 26 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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

Upgrade the Ubuntu dovecot package to 1:2.4.1+dfsg1-5ubuntu4.1.

Patches and advisories

ubuntu.com/security/notices/USN-8136-1 (opens in a new tab)

Affected software

Product	Affected	Fixed in
Ubuntu 25.10dovecot`pkg:deb/ubuntu/dovecot?arch=source&distro=questing`Other threats	Affected <1:2.4.1+dfsg1-5ubuntu4.1	Fixed in 1:2.4.1+dfsg1-5ubuntu4.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Do not clear out the auth_username_chars setting in Dovecot. Install the fixed version 1:2.4.1+dfsg1-5ubuntu4.1 or later as provided by the vendor. The patch is available from the Ubuntu security notice USN-8136-1.

Description

A vulnerability in Dovecot's LDAP authentication allows arbitrary LDAP filter injection if the auth_username_chars setting is empty. This can bypass restrictions and enable probing of the LDAP structure. The issue affects certain versions of Dovecot prior to 1:2.4.1+dfsg1-5ubuntu4.1. A fix is available in version 1:2.4.1+dfsg1-5ubuntu4.1. No public exploits are known.

References

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