CVE-2026-16560

A heap-buffer-overflow flaw was found in Directory Server (389-ds-base). When a DN contains a legacy-quoted value, the server won't close the heap allocation allowing another call to refer to the same memory pointer causing a denial of service or an arbitrary memory write operation.

Red-hat rates this vulnerability as Moderate impact. The function can allow an unauthenticated attacker to send malformed DN requests and trigger the bug. Denial of service is more reliably observed when heap debugging is enabled (for example AddressSanitizer or MALLOC_CHECK_=3), or depending on heap layout and subsequent memory allocator activity. For this reason Red Hat rates availability impact as Low (A:L) rather than High. There is no configuration switch to disable DN normalization for client-supplied DNs.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Denial of service is more reliably observed when heap debugging is enabled (for example AddressSanitizer or MALLOC_CHECK_=3), or depending on heap layout and subsequent memory allocator activity. For this reason Red Hat rates availability impact as Low (A:L) rather than High. There is no configuration switch to disable DN normalization for client-supplied DNs. The vulnerable code path is present in all currently supported 389-ds-base versions that ship the quoted-RDN parsing logic in dn.c.