Metrics
Affected Vendors & Products
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Solution
Upgrade to hMailServer 6.3.8. There a name signs in to an account only when the account's stored address is that name, compared in lower case after a domain alias and the default domain by the function the lockout's key is made with, and a name that reaches the sign-in with white space at either end (POP3's USER takes it off the name it is given, as it always has) signs in to none, whatever the domain aliases hold. Any other spelling fails as a name that does not exist fails, and is counted as such a name is; the country policy asked before the password finds the account by the same rule, so such a spelling meets its domain's policy, as a name that does not exist does. A name a client gives holding a NUL character is refused before any account or domain is looked up with it. Once the password is proved, the lockout, the hold and the country policy of the account whose password it is, and the hold and the country policy of the account signed in to where that is another, as for the IMAP master user, are asked again of the account's own address. The same rule applies to the names a token, a certificate, a Kerberos ticket or an identity provider gives. The password reset keeps its per-address limit under the form of the address that the rule compares and looks up the address it counted, so that a mailbox's recovery address is sent no more links than that limit allows however the address is given. A domain alias's name and the default domain are saved without white space at their ends, and the default domain is read so however it was saved. Until then, an account held for review can be closed by making it inactive, or by changing its password and removing its app passwords, which the sign-in checks on the account it found, whatever spelling it was given, and a domain alias's name or the default domain that ends in white space can be saved again without it. No setting restores the per-name lockout's limit on MySQL, MariaDB, SQL Server or SQL Server Compact; the per-IP auto-ban, on by default, still counts each address's failed sign-ins whatever spelling they use. Keeping the web services listener off (the default) or reachable only from trusted clients keeps names holding a NUL character from the database on Windows; on Linux IMAP LOGIN carries them too.
Workaround
No workaround given by the vendor.
Wed, 11 Nov 2026 08:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | The sign-in of Progressive Robot hMailServer 6.2.22-pre2 through 6.3.7 takes for an account names that are not its address but under which the database's own comparison finds it, while the per-name lockout and the compromised-account hold are kept by the name as the client gave it. This allows a remote unauthenticated attacker to go on guessing an account's password beyond the lockout's threshold, and anyone who has the password of an account held for review to sign in to it. The per-name lockout (from 6.2.22-pre2; AccountLockoutThreshold in hMailServer.ini, 0, off, by default) locks a name after repeated failed sign-ins. The hold (from 6.3.4, where the compromised-account detection is set to enforce, which is not the default) refuses an account judged to have been taken over. Both are asked, before the password, of the name the client gave: trimmed, in lower case and with a domain alias or the default domain applied. The account whose password the sign-in then checks is whichever one the database finds under that name. The databases find an account under spellings that this key counts apart. MySQL and MariaDB find it under one with accented letters in place of plain ones, and MariaDB 11.8, in a database made before 6.3.4, also under one with full-width letters, with a single letter in place of a pair of plain ones, or with characters its comparison ignores in any number. SQL Server and SQL Server Compact find it under one with full-width letters or with characters their comparison ignores in any number, and SQL Server also under one with a single letter in place of a pair of plain ones, with a character of Latin-1 in place of a digit and, for an address holding letters of Latin-1 outside ASCII, under those letters in the other case, and, under an accent-insensitive collation, with accented letters. PostgreSQL finds it under one holding a letter whose lower case under the database's locale is a plain letter, and, for an address holding letters outside ASCII, under those letters in the other case; on the build for musl (from 6.3.6) the server's own lower case folds nearly all of these too. On every database, a domain alias saved with white space at the end of its name gives such a spelling too, and on every database but PostgreSQL so does an account's bare local part where the default domain was saved with spaces at its end and no other white space (neither is the default). Each such spelling has a lockout threshold of its own, so the lockout limits the guesses at an account only to its threshold times the number of the account's spellings. That is far beyond any threshold for most addresses on MySQL and MariaDB, and without limit on SQL Server, on SQL Server Compact, the database the Windows installer uses by default, and before 6.3.4 on MariaDB 11.8. A locked name is got round under another spelling. A held account is signed in to under another spelling with its password over IMAP, POP3 and SMTP AUTH, and, where they are turned on (off by default), over ManageSieve, the REST API and the webmail. IMAP LOGIN, offered as installed, carries such spellings on MySQL, MariaDB and SQL Server Compact, and, on SQL Server and PostgreSQL, for some addresses; the sign-ins that carry a name as UTF-8 carry them for the others on SQL Server, and on PostgreSQL for those holding one of the plain letters another letter lowers to or a letter outside ASCII with another case. The same lookup mapped to accounts the names given by an OAuth 2.0 token, a client certificate, a Kerberos ticket and an OpenID Connect or SAML identity provider, where those are set up (none is by default), so that a name an issuer gave to one party could sign in to another's account; OAuth 2.0 tokens were mapped so from 6.2.0, before the per-name lockout existed. A name holding a NUL character, carried from 6.3.0 on Linux and 6.3.3 on Windows, failed the statement on MySQL, MariaDB and PostgreSQL. | |
| Title | Authentication Bypass by Alternate Name in hMailServer | |
| Weaknesses | CWE-289 | |
| References |
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| Metrics |
cvssV3_1
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Projects
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MITRE
Status: PUBLISHED
Assigner: GitLab
Published:
Updated: 2026-11-11T08:32:57.155Z
Reserved: 2026-11-11T08:04:54.378Z
Link: CVE-2026-126615
Vulnrichment
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NVD
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Redhat
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OpenCVE Enrichment
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