# CVE-2026-126136: OAuth2 access token could be sent over an unencrypted connection with Exchange accounts


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 10 Nov 2026
- **Updated:** 10 Nov 2026
- **Also known as:** DEBIAN-CVE-2026-126136, GHSA-5j3p-5w43-8gwx, UBUNTU-CVE-2026-126136

## What is CVE-2026-126136?

CVE-2026-126136 is a vulnerability in Mozilla Thunderbird, published on 10 Nov 2026. 

### Official description

For Exchange accounts using EWS or Microsoft Graph with OAuth2 authentication, Thunderbird sent the OAuth2 access token to the server even when the configured server URL used unencrypted HTTP. An attacker able to observe network traffic could obtain the token and use it to access the user's mailbox until the token expired. An attacker positioned on the network during account setup could cause such a URL to be configured. This vulnerability was fixed in Thunderbird 160 and Thunderbird 153.7.

## Which versions are affected by CVE-2026-126136?


## How do I fix CVE-2026-126136?

Upgrade to a fixed version.

## Is CVE-2026-126136 being exploited?

There is no known exploitation of CVE-2026-126136 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-126136 and fix it if it is affected.

What it is: CVE-2026-126136 is a vulnerability in Mozilla Thunderbird, published on 10 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-126136 in the wild and no public exploit code.

Affected product: Mozilla Thunderbird. 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-2026-126136/ (Markdown: https://insights.sbomify.com/CVE-2026-126136/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-126136
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126136
- OSV: https://osv.dev/vulnerability/CVE-2026-126136

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-126136/
Summaries are generated and may contain mistakes; the official description above is the record.