High [CVE-2026-90979] LDAPCache and LDAPBackingEngine build LDAP search filters for user lookup and role lookup by textually substituting the placeholders %u, %dn, and %fqdn (drawn from the login name, the resolved user DN, and its fully qualified namespace form) into administrator-configured filter templates (userFilter, roleFilter)

LDAPCache and LDAPBackingEngine build LDAP search filters for user lookup and role lookup by textually substituting the placeholders %u, %dn, and %fqdn (drawn from the login name, the resolved user DN, and its fully qualified namespace form) into administrator-configured filter templates (userFilter, roleFilter).

Before the fix, the only sanitization applied to the substituted value was double backslashed:

filter = filter.replaceAll(Pattern.quote("%u"), Matcher.quoteReplacement(user));

filter = filter.replace("\\", "\\\\");

This does not escape the other characters RFC 4515 requires escaping in an LDAP search filter: *, (, ), and NUL.

A login name containing any of these can change the structure of the resulting filter rather than being matched as a literal value (e.g. a crafted username can turn an equality match into a wildcard match, or close/reopen filter clauses), widening what the search returns and potentially causing a login or role lookup to match an LDAP entry other than the intended one, over-granting roles, and depending on deployment-specific filter templates, potentially affecting which account a login resolved to.

Affected product named by the advisory: Apache Karaf.