Open Babel has heap buffer overflow in SMILES OBSmilesParser::ParseSmiles

Summary

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

Details

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

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 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.

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/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.

Credit

Reported via OSS-Fuzz.