The ldap_utf8prev() function in 389 Directory Server unconditionally reads up to 6 bytes before a heap allocation because it lacks a lower-bound parameter. This API design flaw has existed since the Mozilla LDAP C SDK import and was symptomatically patched twice without fixing the root cause. Twenty call sites remain vulnerable to 1-6 byte heap over-reads.

Cannot be triggered via standard LDAP wire protocol (BER filters parsed separately), but internal callers processing attacker-influenced data (plugin configuration, ACI definitions, replication) are affected. ASan confirmed on aarch64; no crash on production binaries.