Open Babel has out-of-bounds write (overlapping memcpy) in zipstream basic_unzip_streambuf::underflow

Summary

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.

Details

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.

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 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).

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/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.

Credit

Reported via OSS-Fuzz.