CVSS 3.1
5.3 mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:NCVE-2026-126616 Improper Restriction of Excessive Authentication Attempts in hMailServer
Medium (5.3) in progressive robot ltd hmailserver. EPSS 0.4% estimated probability of exploitation activity in the next 30 days.
On this page
The auto-ban of Progressive Robot hMailServer 6.2.0 through 6.3.3, with a MySQL or MariaDB database, can be kept from banning an address after repeated failed logons, which allows a remote unauthenticated attacker to go on guessing account passwords from a single address without being banned. The server makes its MySQL tables in MySQL's utf8 character set, which holds no character outside the Basic Multilingual Plane, sends its statements as UTF-8 over a utf8mb4 connection and leaves the database's default strict mode in place. From 6.2.0 it decodes the user name of a SASL PLAIN logon as UTF-8, so the name can hold such a character. When the failed logons counted from one address reach MaxInvalidLogonAttempts (3 by default), the server clears that address's count, saves an IP range named "Auto-ban: " followed by the user name of the logon that reached the limit, and drops the connection. If such a character is in the part of the user name that the range's name keeps (the name is cut to 100 characters), the database refuses the range: no range is saved, the address is not refused, and, its count having already been cleared, it is given the next full set of attempts. An attacker can in this way spend all but the last attempt of each set on password guesses, and make the last under such a name. On Windows, POP3 AUTH PLAIN reaches it on a server as installed, and IMAP AUTHENTICATE PLAIN where IMAP SASL authentication is turned on (off by default); on Windows and on Linux (from 6.3.0), SMTP AUTH PLAIN reaches it where plain-text authentication is allowed (off by default), and ManageSieve and CardDAV where they are turned on (off by default). Each failed save is reported in the server's error log. A database whose strict mode has been turned off stores the character as a question mark and makes the first such ban, but refuses every later ban named after the same user name, or after one holding other such characters in their place, as a duplicate while the first stands, since the server cannot look up a name holding such a character there.
Severity
- EPSS
- 0.4% estimated probability of exploitation activity in the next 30 days; 35th percentile. Scored 2026-11-13. A forecast for this CVE across the internet, not for your own systems.
- CWE
- CWE-307 Improper Restriction of Excessive Authentication Attempts
- OWASP Top 10
- A07:2025 Authentication Failures
- Published
- Modified
- Assigned by
- GitLab (CNA)
- NVD analysis
- Deferred: the NVD does not plan to analyze it
- Record from
- the NVD, synced
Ask an AI about this CVE
Show the prompt
Explain CVE-2026-126616 for an engineer deciding whether to act. Use https://cve.bz/api/public/cves/CVE-2026-126616?via=ask-ai-copy and https://cve.bz/cve/CVE-2026-126616?via=ask-ai-copy as the source of truth: what is affected and which versions fix it, whether it is in CISA KEV, public exploits, and its EPSS (an internet-wide 30-day estimate of exploitation activity, not a forecast for my systems). If they give no fixed versions, use the CVE record https://cveawg.mitre.org/api/cve/CVE-2026-126616 or the vendor advisory, not third-party mirrors. Tell me how to check whether I am affected and how to verify a fix. Cite the sources and say where they are uncertain.Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this CVE's id and public links.
Badge for a README or a site
An image that stays current: it is drawn from the data each time it is fetched (a host that proxies images, as GitHub does, may show its copy for a while). Markdown:
[](https://cve.bz/cve/CVE-2026-126616)
HTML:
<a href="https://cve.bz/cve/CVE-2026-126616"><img src="https://cve.bz/cve/badge/CVE-2026-126616.svg" alt="CVE-2026-126616"></a>
Affected
- progressive robot ltd:hmailserver
Versions
From the CNA's record in the CVE List.
| Product | Affected |
|---|---|
| Progressive Robot Ltd hMailServer | from 6.2.0 through 6.3.3 |
Attack patterns (CAPEC)
- CAPEC-16 Dictionary-based Password Attack Likelihood: Medium · Severity: High
- CAPEC-49 Password Brute Forcing Likelihood: Medium · Severity: High
- CAPEC-560 Use of Known Domain Credentials Likelihood: High · Severity: High
- CAPEC-565 Password Spraying Likelihood: High · Severity: High
- CAPEC-600 Credential Stuffing Likelihood: High · Severity: High
- CAPEC-652 Use of Known Kerberos Credentials Likelihood: Medium · Severity: High
- CAPEC-653 Use of Known Operating System Credentials Likelihood: High · Severity: High
The attack patterns MITRE's CAPEC relates to this record's weaknesses, as MITRE names them. Credits.
History
- The NVD deferred its analysis
Changes since this site first stored the record. The same for every record: /api/public/changes.