High [CVE-2026-73194] DBI for Perl: Heap out-of-bounds write via unvalidated numeric placeholder

DBI versions before 1.652 for Perl allow a heap out-of-bounds write via an unvalidated numeric placeholder that sets the binder counter in preparse. preparse reserves seven output bytes per input byte, the width of the longest ':p99999' expansion.

The ':N' branch parses the number with `atoi(src)` and assigns it to the binder counter with no range check, so a statement containing ':2147483648' leaves the counter negative (-2147483648 with glibc, where atoi wraps).

Each following '?' then expands through `sprintf(start, ":p%d", idx++)` to ':p-2147483648', 14 bytes with the terminating NUL where the buffer budgets 7. The placeholder limit added in 1.650 tests the counter against 99,999, which a negative counter passes.

Any caller that preparses an untrusted statement into ':pN' style placeholders gets a heap out-of-bounds write that grows with the number of '?' marks following the poisoned placeholder. The '?' and '%s' return styles compare the parsed number against the expected sequence and error out, and are unaffected.

When processing an untrusted statement, a specially crafted numeric placeholder can cause the binder counter to become negative. This results in subsequent placeholders expanding beyond their allocated buffer, leading to memory corruption.

An attacker could exploit this to potentially achieve arbitrary code execution or cause a denial of service.