Heap buffer overflow via wrapped size check during SASL username canonicalization

Medium5.7CVE-2026-88035 · Published Sep 11, 2026

### Impact A size check in the client-side authentication path of the MongoDB C Driver can wrap around, so an unusually large user-name value is accepted and copied past the end of a small buffer. A party able to set the driver's connection settings may cause the application that embeds the driver to terminate unexpectedly. Reaching this code requires a build in which the optional external SASL authentication backend is present and a connection configured to use it. ### Patches Fixed in 2.5.3. ### Workarounds Validate username. ### References https://jira.mongodb.org/browse/CDRIVER-6416