Open Babel has a NULL pointer dereference in CDXML OBAtom::GetExplicitValence
Date: 2026-06
Affected: pip/openbabel
Attack vector: dos
Category: vulnerability-disclosure
Severity: Low
CVE: CVE-2026-3408
CWE: CWE-404
CWE-476
CWE-787
CVSS: 5.5 (CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H)

### Summary A memory-safety vulnerability in Open Babel's CDXML file format parser caused a NULL pointer dereference when reading a crafted input file. ### Details The flaw was in `OBAtom::GetExplicitValence` as called from the CDXML parser. A malformed fragment caused the parser to invoke the method on a NULL atom pointer. ### 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 CDXML 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/e23a224b Tracked in #2862. 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 by Vedant Madane (@VedantMadane) via VulDB.


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