High [CVE-2026-15722] pre-authentication stack buffer overflow in get_ruvelement_from_berval via unbounded replica ID parsing

A stack buffer overflow flaw was found in 389 Directory Server (389-ds-base). The get_ruvelement_from_berval() function in repl5_ruv.c copies digit characters from a network-supplied RUV berval into a fixed 16-byte stack buffer without bounds checking.

A remote unauthenticated attacker can crash the LDAP server by sending a crafted StartNSDS50ReplicationRequest extended operation containing a replica ID field with more than 16 digit characters. The overflow occurs during payload decoding, before any authorization check.

Stack protectors limit impact to denial of service. The overflow data is limited to ASCII digit characters and a null byte.

Stack protectors and ASLR prevent the overflow from being leveraged for code execution — the stack canary detects the corruption and aborts the process. The practical impact is therefore limited to denial of service.

Customers who have restricted network access to the LDAP port to trusted replication partners, or who have disabled anonymous access by setting nsslapd-allow-anonymous-access to 'off' or 'rootdse', are not exposed to unauthenticated exploitation of this flaw. Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Weakness: CWE-121.