Answer in brief
CVE-2026-126616 records a Medium severity (CVSS 5.3) vulnerability in Improper Restriction of Excessive Authentication Attempts in hMailServer. The current sources do not mark it as known exploited. The current feed maps Progressive Robot Ltd/hMailServer (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 5.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Progressive Robot Ltd/hMailServer (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Progressive Robot Ltd/hMailServergeneric | >=6.2.0 <=6.3.3 | Not reported |
Published upstream
Nov 11, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Nov 11, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Nov 11, 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 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.
Quoted source text, attributed separately from HOL analysis.