CVE-2026-96749Heap out-of-bounds write via signed size overflow in BSON document encoding

Official description

An integer overflow in the BSON document encoding component of the MongoDB Python Driver's bundled native extension may occur when a single document is built from an unusually large amount of caller-supplied data. Size arithmetic is performed in a signed 32-bit type, and the guard meant to catch the overflow is written in a form whose behavior is not defined by the C language standard. A party with no privileges who can place a very large value into data that an application encodes may, depending on how the native extension was built, cause a write outside the bounds of an allocated buffer inside the application's own process.

Affected packages & fixed versions

Affected products (as reported)

References

• https://github.com/mongodb/mongo-python-driver/security/advisories/GHSA-v4x9-3549-crwv
• https://github.com/mongodb/mongo-python-driver/releases/tag/4.18.2
• https://github.com/mongodb/mongo-python-driver/blob/4.18.2/doc/changelog.rst