CVE-2026-126136 OAuth2 access token could be sent over an unencrypted connection with Exchange accounts
- Exploited in the wild
- Not known
- Fix
- Available
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.
Sources
Also known as DEBIAN-CVE-2026-126136, GHSA-5j3p-5w43-8gwx, UBUNTU-CVE-2026-126136.