CVE-2026-126616VulnerabilityPublished 11 Nov 2026

The auto-ban of Progressive Robot hMailServer 6.2.0 through 6.3.3, with a MySQL or MariaDB database, can be kept from

Source GCVE Database

Compare

Authoritative record:CVE-2026-126616· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium.

Data as of 11 Nov 2026, 10:04 UTC

CVSS 3.1 base score

5.3Medium

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

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitLab)	CVSS 3.1	5.3

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

Attack Vector: Network
Attack Complexity: Low
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: 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: 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 11 Nov 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 10 Nov 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.

ghsa-4f2q-v3rq-2852

What to do

Affected software

Product	Affected	Fixed in
Progressive Robot LtdhMailServer	Affected >=6.2.0 <=6.3.3	Fixed in–
GitHubhmailserver/hmailserver`pkg:github/hmailserver/hmailserver`Other threats	Affected >=6.2.0 <=6.3.3	Fixed in–

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

AI-suggested

Administrators should review authentication configurations and consider disabling or restricting authentication methods that allow usernames with characters outside the Basic Multilingual Plane. Monitoring error logs for failed ban saves may help detect exploitation attempts. Since the vulnerability arises from character set handling in the database and server, adjusting database strict mode or character set settings may mitigate the issue but could introduce other risks. Follow vendor advisories for updates and patches.

Description

A vulnerability in hMailServer versions 6.2.0 through 6.3.3 using MySQL or MariaDB databases allows an attacker to bypass the auto-ban mechanism after repeated failed login attempts. This occurs because the server's auto-ban feature fails to save IP ranges when usernames contain certain UTF-8 characters outside the Basic Multilingual Plane, preventing bans from being enforced. As a result, an unauthenticated remote attacker can continue guessing passwords from a single IP address without being banned. The issue affects authentication methods using SASL PLAIN and plain-text authentication under certain configurations. Failed attempts to save bans are logged as errors. The CVSS score is 5.3 (medium severity).

Impact

An unauthenticated remote attacker can bypass the auto-ban mechanism designed to limit repeated failed login attempts from the same IP address. This allows the attacker to perform password guessing attacks without being blocked, increasing the risk of unauthorized access. The impact is limited to information disclosure (password guessing) with no direct integrity or availability impact reported.

Summary

hMailServer versions 6.2.0 through 6.3.3 with MySQL or MariaDB backends are vulnerable to bypass of the auto-ban feature that limits failed login attempts per IP address. The server uses MySQL's utf8 character set for tables but communicates over a utf8mb4 connection and decodes usernames as UTF-8, allowing characters outside the Basic Multilingual Plane in usernames. When a username containing such characters triggers the auto-ban, the database rejects saving the IP range due to character set incompatibility, causing the ban not to be recorded and the failed login count to reset. This allows an attacker to repeatedly guess passwords from the same IP without being banned. The vulnerability affects POP3 AUTH PLAIN (Windows), IMAP AUTHENTICATE PLAIN (Windows), SMTP AUTH PLAIN (Windows and Linux from 6.3.0), and optionally ManageSieve and CardDAV where enabled. The server logs errors for each failed ban save. Disabling strict mode in the database causes the first ban to succeed but subsequent bans to be rejected as duplicates. No public exploits or patches are currently reported.

CWE-307Improper Restriction of Excessive Authentication Attempts (opens in a new tab)
Base weaknessOWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
The product does not implement sufficient measures to prevent multiple failed authentication attempts within a short time frame.
Architecture and Design
Common protection mechanisms include: Disconnecting the user after a small number of failed attempts; Implementing a timeout; Locking out a targeted account; Requiring a computational task on the user's part.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
Authentication (opens in a new tab)
Transport Layer Protection (opens in a new tab)
TLS Cipher String (opens in a new tab)
OWASP ASVS 4.0.3
V2.2.1 (opens in a new tab)
V2.8.5 (opens in a new tab)
V2.8.4 (opens in a new tab)
Attack patterns
Dictionary-based Password Attack (opens in a new tab)
Password Brute Forcing (opens in a new tab)
Password Spraying (opens in a new tab)
Credential Stuffing (opens in a new tab)
Use of Known Kerberos Credentials (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 11 Nov 2026, 10:04 UTC

WeaknessesCWE-307

Technical details

References

Community reviews

Related threats