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Fencer Intel
no cvss —

CVE-2026-126136 json

OAuth2 access token could be sent over an unencrypted connection with Exchange accounts

published yesterday modified yesterday also EUVD-2026-122690

cvss
—
not scored
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 15%
public exploits
0
none known

Summary

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.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-126136 updated cvss 6.1

thunderbird: OAuth2 access token could be sent over an unencrypted connection with Exchange accounts

  • Red Hat Enterprise Linux 6 thunderbird Red Hat Enterprise Linux 7 thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 thunderbird Red Hat Enterprise Linux 9 thunderbird Red Hat Enterprise Linux 10 thunderbird, rhel10/thunderbird-flatpak
    affected: no fix available

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.24% chance of exploitation in the next 30 days, higher than 15% of all scored CVEs (FIRST EPSS, 2026-11-11).

Affected products

  • Mozilla Thunderbird

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.