A heap buffer underflow occurs in the readline() function of the LMDB component of OpenLDAP. When malformed input containing an embedded NUL byte is processed, an unsigned offset calculation wraps around and triggers an out‑of‑bounds read of a single byte immediately before the allocated buffer. The result is a crash of the mdb_load utility, causing a limited denial‑of‑service condition. The weakness is a classic buffer underflow (CWE‑125) that can also lead to unsigned integer underflow (CWE‑191).

Vulnerable versions include OpenLDAP Lightning Memory‑Mapped Database (LMDB) through 0.9.14, as well as any OpenLDAP releases prior to the commit identified as 8e1fda8. The affected vendor is the OpenLDAP Foundation, with the product named OpenLDAP.

The CVSS score of 4.6 indicates moderate severity, and the EPSS score of less than 1% suggests a low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. Attacks would require an attacker to supply crafted input to the mdb_load utility; the effect is isolated to the process, resulting in a crash rather than arbitrary code execution.