Is CVE-2026-126136 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-126136 being exploited in the wild.

How severe is CVE-2026-126136?

Informational severity, published 10 November 2026.

Which products and versions are affected?

Mozilla Thunderbird before 160.

Is there a fix for CVE-2026-126136?

Yes: fixed in Thunderbird 160. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-126136 attacked?

It is attacked over the network or from the adjacent network, in a web application.

Am I affected by CVE-2026-126136?

Check whether you run Mozilla Thunderbird at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-126136: Thunderbird OAuth2 access token leak over HTTP with Exchange accounts

CVE-2026-126136 · Severity: info · Published 2026-11-10

Thunderbird, an email and calendar client, sent OAuth2 access tokens to Exchange servers in cleartext over unencrypted HTTP connections when configured with Microsoft Exchange accounts. An attacker on the network could intercept these tokens and gain access to the user's mailbox for as long as the token remained valid. This could occur if an attacker manipulated the account setup process to configure an HTTP URL instead of HTTPS.

Technologies: Mozilla Thunderbird. Vendors: Mozilla.

Quick answers

Is CVE-2026-126136 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-126136 being exploited in the wild.
How severe is CVE-2026-126136?: Informational severity, published 10 November 2026.
Which products and versions are affected?: Mozilla Thunderbird before 160.
Is there a fix for CVE-2026-126136?: Yes: fixed in Thunderbird 160. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-126136 attacked?: It is attacked over the network or from the adjacent network, in a web application.
Am I affected by CVE-2026-126136?: Check whether you run Mozilla Thunderbird at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

Fixed in: Thunderbird 160

Technical details

When using EWS or Microsoft Graph OAuth2 authentication with Exchange accounts, Thunderbird failed to enforce HTTPS and sent the OAuth2 access token over unencrypted HTTP. An attacker with network visibility could passively capture the token via traffic interception or active MITM, and subsequently use it to authenticate to the user's mailbox until token expiration. The vulnerability was fixed in Thunderbird 160.

Affected products

Mozilla Thunderbird before 160

Timeline

2026-11-10: disclosed: CVE-2026-126136

References

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