What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 8.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-24 · updated 2026-09-26
• Weakness: CWE-190

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 products

• MongoDB Python Driver: from 1.9.0 before 4.18.2 — fixed in 4.18.2

How to fix

Upgrade to a fixed version: MongoDB Python Driver 4.18.2. Check the vendor advisory for mitigations.

References

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

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