CVE-2018-20840: Google API C++ Client

High severity, CVSS 8.6. EPSS: 0.7% chance of exploitation in the next 30 days.

An unhandled exception vulnerability exists during Google Sign-In with Google API C++ Client before 2019-04-10. It potentially causes an outage of third-party services that were not designed to recover from exceptions. On the client, ID token handling can cause an unhandled exception because of misinterpretation of an integer as a string, resulting in denial-of-service and then other users can no longer login/sign-in to the affected third-party service. Once this third-party service uses Google Sign-In with google-api-cpp-client, a malicious user can trigger this client/auth/oauth2_authorization.cc vulnerability by requesting the client to receive the ID token from a Google authentication server.

Affected products

• Google API C++ Client: before 2019-04-10 (fixed in 2019-04-10)

Published 2019-05-30. Last modified 2026-06-17.