VulnerabilityPublished 11 Nov 2026

CVE-2026-126614: Progressive Robot hMailServer · Improper Restriction of Excessive Authentication Attempts

Affects Progressive Robot hMailServerSource CVE Database V5

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Not known to be exploited · CVSS 5.3 Medium.

Data as of 11 Nov 2026, 08:50 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.

What to do

Affected software

Product	Affected	Fixed in
Progressive Robot LtdhMailServer	Affected >=6.3.3 <=6.3.7	Fixed in–

AI-suggested

The web services listener is off by default (WebServicesHttpPort and WebServicesHttpsPort set to 0), so disabling it if not needed mitigates exposure. Review and update firewall rules and fail2ban configurations to include the web services listener ports if enabled. Monitor vendor advisories for any forthcoming patches or official fixes. Avoid placing the listener behind TLS-terminating proxies without additional client IP forwarding mechanisms to enable effective banning.

Description

Progressive Robot Ltd hMailServer versions 6.3.3 through 6.3.7 have a vulnerability in the web services listener where IP-based auto-ban restrictions are not applied. This allows remote unauthenticated attackers to continue guessing account passwords via the listener's sign-in interface even after their IP address has been banned on other protocols. The listener does not enforce IP bans properly, enabling repeated authentication attempts behind TLS-terminating proxies or from banned IPs. The flaw affects the CardDAV, CalDAV, and Outlook Autodiscover services over HTTPS. The vulnerability has a medium severity with a CVSS score of 5.3 and does not have known exploits in the wild. The listener is off by default, and no official patch information is provided in the data.

Impact

An attacker can perform unlimited password guessing attempts against user accounts via the web services listener even after their IP address has been banned on other protocols. This increases the risk of successful brute-force attacks on account credentials. The vulnerability affects authentication services over HTTPS and can be exploited remotely without authentication. However, the listener is off by default, which may reduce exposure. There is no indication of direct data compromise or denial of service from this vulnerability alone.

Summary

The web services listener in Progressive Robot Ltd hMailServer versions 6.3.3 through 6.3.7 fails to apply the server's IP range restrictions to incoming connections. This allows attackers to bypass the auto-ban mechanism that normally blocks IP addresses after multiple failed login attempts on SMTP, POP3, IMAP, and ManageSieve protocols. The listener accepts connections without enforcing IP bans, permitting unlimited password guessing attempts via HTTP Basic authentication over HTTPS on CardDAV (from 6.3.3), CalDAV, and Outlook Autodiscover (from 6.3.4). The auto-ban firewall rules and fail2ban configurations do not cover the web services listener ports, further enabling this bypass. Additionally, behind TLS-terminating proxies, the listener sees only the proxy's IP, preventing effective banning of the actual client IP. The vulnerability is identified as CWE-307 (Improper Restriction of Excessive Authentication Attempts) and has a CVSS 3.1 base score of 5.3 (medium severity).

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

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 11 Nov 2026, 08:50 UTC

WeaknessesCWE-307

Technical details

References

Community reviews

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