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Fencer Intel
no cvss —

CVE-2026-126133 json

Calendar server credentials could be sent to an HTTP proxy

published yesterday modified yesterday also EUVD-2026-122687

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 11%
public exploits
0
none known

Summary

When a CalDAV or ICS calendar was accessed through an HTTP proxy that requested authentication, Thunderbird could answer the proxy with the calendar server's username and password. This affected both setting up a new calendar and syncing existing calendars, where a saved password could be sent without any user interaction. A malicious or compromised proxy could use this to obtain the calendar credentials, even for calendars served over HTTPS. 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-2026-126133 updated cvss 6.1

thunderbird: Calendar server credentials could be sent to an HTTP proxy

  • 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

0.21% chance of exploitation in the next 30 days, higher than 11% 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.