PYSEC-2026-2781

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.