# CVE-2018-20840: Denial of service in n/a

> A malicious user can trigger an unhandled exception in the Google API C++ Client during sign-in, causing a denial of service for third-party services.

- **Severity:** High 8.6 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 30 May 2019
- **Updated:** 5 Aug 2024
- **Also known as:** GHSA-jw9r-r4mj-mpxx

## What is CVE-2018-20840?

CVE-2018-20840 is a high-severity denial of service vulnerability in n/a, published on 30 May 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-754 (Improper Check for Unusual or Exceptional Conditions)

## Which versions are affected by CVE-2018-20840?

It affects 1 product.


Products: Google Api C\+\+ Client.

## How do I fix CVE-2018-20840?

No fix has been published for CVE-2018-20840 yet. Limit exposure of the affected software until one is available.

## Is CVE-2018-20840 being exploited?

There is no known exploitation of CVE-2018-20840 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-20840 and fix it if it is affected.

What it is: CVE-2018-20840 is a high-severity denial of service vulnerability in n/a, published on 30 May 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2018-20840 in the wild and no public exploit code.

Affected product: n/a. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2018-20840/ (Markdown: https://insights.sbomify.com/CVE-2018-20840/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-20840
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-20840
- OSV: https://osv.dev/vulnerability/CVE-2018-20840

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-20840/
Summaries are generated and may contain mistakes; the official description above is the record.