GHSA-j35x-w4gj-pf7w

### 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.