A memory-safety vulnerability in Open Babel's bundled zipstream decompression code caused an out-of-bounds write via overlapping memcpy when reading a crafted gzip-compressed chemistry file.

The flaw was in basic unzip streambuf::underflow. The decompression buffer refill path invoked memcpy with overlapping source and destination regions, which is undefined behavior and produced out-of-bounds writes in practice. Any file format read through the gzip-wrapped reader was a potential trigger.

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 gzip-compressed chemistry file with the obabel tool, the OBConversion API, or any of the language bindings (Python, Ruby, Java, R, Perl, C#, PHP).

All releases up to and including 3.1.1.

3.2.0 (released 2026-05-26).

Fix commit: https://github.com/openbabel/openbabel/commit/d4621d41 Originally reported as #2832; 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.