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

Published Nov 10, 2026
·
Updated

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.

Affected Software

1 affected componentFixes available
Mozilla Thunderbird<160
160

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 160
  2. Upgrade

    Upgrade Thunderbird to a version that resolves this vulnerability.

    Fixed in 160

Event History

Nov 10, 2026
CVE Published
via Mozilla·12:00 AM
Data Sourced
via Mozilla·12:00 AM
DescriptionSeverityAffected Software
CVE Published
via MITRE·06:59 PM
Data Sourced
via MITRE·06:59 PM
Description
Data Sourced
via NVD·07:21 PM
Description

Parent advisories

This vulnerability appears in the following advisories.

Peer vulnerabilities

Found alongside the following vulnerabilities.

Frequently Asked Questions

1

Which Thunderbird configurations are exposed?

The issue affects Exchange accounts that use EWS or Microsoft Graph with OAuth2 authentication when their configured server URL uses unencrypted HTTP. Accounts using other protocols or authentication methods are not identified as affected by the provided information.

2

What does an attacker need to exploit this?

An attacker must be able to observe network traffic to capture the OAuth2 access token sent over HTTP. An attacker positioned on the network during account setup could also cause an unencrypted server URL to be configured.

3

What is the impact if a token is captured?

A captured OAuth2 access token can be used to access the user's mailbox until that token expires.

4

How can this be remediated?

Update to Thunderbird 160, where this issue was fixed. Also ensure affected Exchange EWS or Microsoft Graph account server URLs use encrypted HTTPS rather than HTTP.

Company

Resources

Contact

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