Yamcs CVE-2026-42568

Summary

An LDAP injection vulnerability exists in org.yamcs.security.LdapAuthModule when constructing search filters. The username parameter is inserted directly into the LDAP filter without proper RFC 4515 escaping.

Root Cause

File: yamcs-core/src/main/java/org/yamcs/security/LdapAuthModule.java:233

The username parameter is inserted directly into an LDAP search filter without RFC 4515 escaping:

// VULNERABLE
var filter = userFilter.replace("{0}", username);
var searchResult = getSingleResult(ctx, userBase, filter, controls);

LDAP wildcard characters (*, (, )) are accepted without sanitization.

Impact

With a known valid password, username=* authenticates as the first user returned by the LDAP search - enabling horizontal privilege escalation between accounts sharing similar passwords or when the attacker knows one valid password.

This affects deployments that use org.yamcs.security.LdapAuthModule in their etc/security.yaml configuration file.

Proof of Concept

curl -X POST "http://TARGET:8090/auth/token" \
  -d "grant_type=password&username=*&password=known_password"
# Returns token for first matching LDAP user

Fix

Apply RFC 4515 escaping before filter construction:

private static String escapeLdapFilter(String input) {
    return input
        .replace("\\", "\\5c")
        .replace("*",  "\\2a")
        .replace("(",  "\\28")
        .replace(")",  "\\29")
        .replace("\0", "\\00");
}
var filter = userFilter.replace("{0}", escapeLdapFilter(username));