How severe is CVE-2018-20840?

CVE-2018-20840 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2018-20840 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (47th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2018-20840?

CVE-2018-20840 affects Google Api C++ Client. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2018-20840?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2018-20840 published?

CVE-2018-20840 was published on 2019-05-30 and last updated on 2026-06-17.

CVE-2018-20840

CVE-2018-20840 is a high-severity vulnerability in Google Api C++ Client with a CVSS 3.x base score of 8.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-754.

Key facts

Severity: High (CVSS 3.x base score 8.6)
CVSS v2: 5.0
EPSS exploit prediction: 1% (47th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-754
Affected product: Google Api C++ Client
Published: 2019-05-30
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2018-20840?: 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.
How severe is CVE-2018-20840?: CVE-2018-20840 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2018-20840 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (47th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2018-20840?: CVE-2018-20840 affects Google Api C++ Client. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2018-20840?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2018-20840 published?: CVE-2018-20840 was published on 2019-05-30 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:google:api_c\+\+_client:*:*:*:*:*:*:*:*

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