Heap buffer overflow via wrapped size check during SASL username canonicalization

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