As per upstream:

A DN may be represented in string form with arbitrary amounts of space around the component values. These spaces are supposed to be ignored, but invalid DNs strings with spaces may instead cause a zero byte to
be written into out-of-bounds memory.

An LDAP bind request can send a string DN as a username. This DN is necessarily parsed before the password is checked, so an attacker without real credentials can anonymously trigger this bug.

The location of zero byte is a negative offset relative to the location of a dynamically allocated heap buffer; the exact offset depends on the DN string. While it is possible for an attacker to cause non-fatal data corruption, usefully targeting this is likely to be difficult and the most likely outcome is a crash.

The affected parsing routine is widely used. LDAP bind is not the only way to trigger the bug remotely, though it appears to be the only unauthenticated method.