A memory-safety vulnerability in Open Babel's SMILES parser caused a heap buffer overflow when reading a crafted input string.

The flaw was in OBSmilesParser::ParseSmiles. A malformed SMILES input caused the parser to write past the end of a heap-allocated buffer.

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 parse a malicious SMILES string with the obabel tool, the OBConversion API, or any of the language bindings (Python, Ruby, Java, R, Perl, C#, PHP). SMILES strings are commonly passed on the command line and through scripted pipelines, so this primitive is especially reachable.

All releases up to and including 3.1.1.

3.2.0 (released 2026-05-26).

Fix commit: https://github.com/openbabel/openbabel/commit/b34cd604 Originally reported as #2831; 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.

Reported via OSS-Fuzz.