CVE-2026-106431: CWE-787: Out-of-bounds Write in MongoDB C Driver

This vulnerability is an off-by-one error in the BSON bulk document writer component of the MongoDB C Driver. When a document ends at a precise buffer boundary, the driver writes a zero byte immediately beyond the allocated heap buffer, resulting in an out-of-bounds write. Exploitation requires the embedding application to use the BSON bulk-writer API and to produce documents with carefully controlled sizes. The flaw can cause memory corruption or crash the process.

An attacker who can influence the size of BSON documents serialized by an application using the vulnerable MongoDB C Driver versions can trigger an out-of-bounds write. This may corrupt adjacent process memory or cause the process to terminate unexpectedly. There is no indication of remote exploitability without local access or influence over document sizes. No known exploits are reported in the wild.

No official patch or fix is currently documented in the provided data. Users should monitor MongoDB vendor advisories for updates. Until a fix is available, avoid using the BSON bulk-writer API with untrusted input that could produce documents ending at the specific buffer boundary triggering the off-by-one write.