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CVE Record

CVE-2018-20840: An unhandled exception vulnerability exists during Google Sign-In with Google API C++ Client before 2019-04...

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.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This flaw can let a malicious login attempt crash Google Sign-In handling in third-party services using the Google API C++ Client. The business impact is service denial: legitimate users may be unable to sign in until the affected service recovers or is fixed.

Executive priority

Treat this as a targeted availability risk for login-dependent services. Prioritize if customer access, support operations, or revenue workflows depend on Google Sign-In through the affected C++ client.

Technical view

In google-api-cpp-client before 2019-04-10, ID token handling in client/auth/oauth2_authorization.cc can misinterpret an integer as a string, causing an unhandled exception. Services that do not recover from that exception can suffer authentication denial-of-service.

Likely exposure

Exposure is likely limited to third-party C++ services using google-api-cpp-client for Google Sign-In, particularly code predating 2019-04-10. The CVE bundle does not identify specific downstream products, CPEs, or packaged versions.

Exploitation context

The sources describe a malicious user triggering the flaw by causing the client to receive an ID token from a Google authentication server. KEV is false, and the bundle provides no evidence of active exploitation in the wild.

Researcher notes

The public bundle lacks CVSS, CWE, CPE, affected product metadata, and exploit-in-the-wild evidence. Analysis should stay scoped to google-api-cpp-client Google Sign-In ID token handling and the referenced GitHub issue and pull request.

Mitigation direction

  • Identify services using google-api-cpp-client for Google Sign-In.
  • Update google-api-cpp-client to code released after 2019-04-10.
  • Review the linked Google issue and pull request for exact fix context.
  • Add exception handling around authentication paths where operationally appropriate.
  • Check vendor or project guidance before deploying compensating controls.

Validation and detection

  • Inventory C++ services that implement Google Sign-In.
  • Confirm google-api-cpp-client source or package date is after 2019-04-10.
  • Review authentication error handling for unrecovered exceptions.
  • Check monitoring for sign-in outage patterns tied to token handling.
  • Validate remediation in staging with safe negative authentication tests.
Prepared
Confidence
medium
Sources
4

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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Credential and access behavior lookup

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CVE-2018-20840 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
3Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

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