An integer overflow occurs in the BSON document encoding component of the MongoDB Python Driver’s bundled native extension when a single document contains an unusually large amount of caller‑supplied data. Signed 32‑bit arithmetic is used, and the guard intended to detect the overflow is written in a form whose behavior is undefined by the C language standard, allowing a write outside the bounds of an allocated buffer. A party with no special privileges who can supply a sufficiently large value for data that an application encodes can, depending on how the native extension was built, corrupt memory inside the application’s own process.

The vulnerability affects the MongoDB Python Driver, with all releases prior to 4.18.2 impacted. The fix is included in version 4.18.2, which should be deployed by all users of the driver.

The CVSS score of 7.5 indicates high severity, and the EPSS score is < 1%, indicating a low probability of exploitation, while the vulnerability is not yet listed in CISA’s KEV catalog. The likely attack vector involves an attacker manipulating data that an application sends to the driver; no elevated privileges are required, but the attacker must be able to influence the content of a BSON document that is subsequently encoded. Exploitation may depend on build configuration of the native extension. Overall, the risk is significant due to the potential for arbitrary memory corruption and possible execution of malicious code, so timely remediation is warranted.