Open Babel has NULL pointer dereference in CACAO CacaoFormat::SetHilderbrandt

Summary

A memory-safety vulnerability in Open Babel's CACAO parser caused a
NULL pointer dereference when reading a crafted input file.

Details

The flaw was in CacaoFormat::SetHilderbrandt. A malformed input
caused the parser to dereference a NULL pointer while applying the
Hilderbrandt transformation.

Impact

Open Babel is a C++ library and CLI used to read and write chemistry
file formats; it is shipped by Linux distributions and embedded in
services that may parse untrusted input. Triggering this vulnerability
requires the victim to open a malicious CACAO file with the obabel
tool, the OBConversion API, or any of the language bindings (Python,
Ruby, Java, R, Perl, C#, PHP).

Affected versions

All releases up to and including 3.1.1.

Patched version

3.2.0 (released 2026-05-26).

Patch

Fix commit: https://github.com/openbabel/openbabel/commit/ecaed96f
Originally reported as #2827; fixes consolidated in #2913.

A minimized reproducer for this CVE is checked in under
test/files/fuzz_regress/ and is exercised on every CI build under
ASAN+UBSAN by the fuzzregresstest harness.

Credit

Reported via OSS-Fuzz.