CVE-2026-88035: Heap buffer overflow via wrapped size check during SASL username canonicalization in MongoDB C Driver
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.
Affected Software
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Exposure requires a MongoDB C Driver build with the optional external SASL authentication backend present, and a connection configured to use that backend. Deployments without that build option or without such a connection configuration do not reach the affected code path.
What level of access does an attacker need?
The attacker must be able to set the driver's connection settings and supply an unusually large user-name value. The provided information indicates the consequence is unexpected termination of the application embedding the driver.