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Fencer Intel
high 8.1

CVE-2025-3909 json

JavaScript Execution via Spoofed PDF Attachment and file:/// Link

published last yr. modified 4mo ago also EUVD-2025-14935

cvss
8.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 40%
public exploits
0
none known

Summary

Thunderbird's handling of the X-Mozilla-External-Attachment-URL header can be exploited to execute JavaScript in the file:/// context. By crafting a nested email attachment (message/rfc822) and setting its content type to application/pdf, Thunderbird may incorrectly render it as HTML when opened, allowing the embedded JavaScript to run without requiring a file download. This behavior relies on Thunderbird auto-saving the attachment to /tmp and linking to it via the file:/// protocol, potentially enabling JavaScript execution as part of the HTML. This vulnerability was fixed in Thunderbird 128.10.1 and Thunderbird 138.0.1.

Patch / fix

  • mozilla thunderbird 128.10.1, 138.0.1
  • mozilla thunderbird_esr 128.10.1, 138.0.1
  • thunderbird Debian 12 1:128.10.1esr-1~deb12u1
  • thunderbird Debian 14, Debian 13 1:128.10.1esr-1

debian advisories DEBIAN-CVE-2025-3909

  • thunderbird Ubuntu 22.04 LTS 1:128.12.0+build1-0ubuntu0.22.04.1

ubuntu advisories UBUNTU-CVE-2025-3909

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • thunderbird RHEL 8 128.11.0-1.el8_10
  • thunderbird RHEL 9 128.10.1-1.el9_6
  • thunderbird RHEL 10.0 128.10.1-1.el10_0
  • thunderbird RHEL 8.8 TUS, RHEL 8.8 E4S 128.10.1-1.el8_8
  • thunderbird RHEL 8.6 TUS, RHEL 8.6 E4S, RHEL 8.6 AUS 128.10.1-1.el8_6
  • thunderbird RHEL 8.4 AUS 128.10.1-1.el8_4
  • thunderbird RHEL 8.2 AUS 128.10.1-1.el8_2
  • thunderbird RHEL 9.2 EUS 128.10.1-1.el9_2

red hat advisories RHSA-2025:8756RHSA-2025:8784RHSA-2025:8594RHSA-2025:8507RHSA-2025:8391RHSA-2025:8326

  • MozillaThunderbird SLE Workstation Extension 15 SP7, SLE Workstation Extension 15 SP6, SLE Module for Package Hub 15 SP7 +2 more 128.10.1-150200.8.215.1

suse advisories SUSE-SU-2025:01660-2SUSE-SU-2025:01660-1

  • MozillaThunderbird openSUSE Tumbleweed 128.10.1-1.1

opensuse advisories openSUSE-SU-2025:15131-1

  • thunderbird AlmaLinux 8 128.11.0-1.el8_10.alma.1
  • thunderbird AlmaLinux 10 128.10.1-1.el10_0.alma.1

almalinux advisories ALSA-2025:8756ALSA-2025:8196

  • thunderbird Rocky Linux 9 128.10.1-1.el9_6
  • thunderbird Rocky Linux 10 128.10.1-1.el10_0
  • thunderbird Rocky Linux 8 128.11.0-1.el8_10

rocky linux advisories RLSA-2025:8203RLSA-2025:8196RLSA-2025:8756

Is CVE-2025-3909 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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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-2025-3909 updated cvss 6.5

thunderbird: JavaScript Execution via Spoofed PDF Attachment and file:/// Link

  • Red Hat Enterprise Linux 6 thunderbird Red Hat Enterprise Linux 7 thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 10 thunderbird-flatpak
    affected: no fix available
  • Red Hat Enterprise Linux AppStream (v. 8) thunderbird 128.11.0-1.el8_10
    fixed: vendor fix RHSA-2025:8756
  • Red Hat Enterprise Linux AppStream (v. 9) thunderbird 128.10.1-1.el9_6
    fixed: vendor fix RHSA-2025:8203
  • Red Hat Enterprise Linux AppStream (v. 10) thunderbird 128.10.1-1.el10_0
    fixed: vendor fix RHSA-2025:8196
  • Red Hat Enterprise Linux AppStream AUS (v. 8.2) thunderbird 128.10.1-1.el8_2
    fixed: vendor fix RHSA-2025:8391
  • Red Hat Enterprise Linux AppStream AUS (v.8.4) thunderbird 128.10.1-1.el8_4
    fixed: vendor fix RHSA-2025:8507
  • Red Hat Enterprise Linux AppStream AUS (v.8.6) thunderbird 128.10.1-1.el8_6 Red Hat Enterprise Linux AppStream E4S (v.8.6) thunderbird 128.10.1-1.el8_6
    fixed: vendor fix RHSA-2025:8594
show 6 more
  • Red Hat Enterprise Linux AppStream E4S (v.8.8) thunderbird 128.10.1-1.el8_8
    fixed: vendor fix RHSA-2025:8784
  • Red Hat Enterprise Linux AppStream E4S (v.9.0) thunderbird 128.10.1-1.el9_0
    fixed: vendor fix RHSA-2025:8324
  • Red Hat Enterprise Linux AppStream EUS (v.9.2) thunderbird 128.10.1-1.el9_2
    fixed: vendor fix RHSA-2025:8326
  • Red Hat Enterprise Linux AppStream EUS (v.9.4) thunderbird 128.10.1-1.el9_4
    fixed: vendor fix RHSA-2025:8325
  • Red Hat Enterprise Linux AppStream TUS (v.8.6) thunderbird 128.10.1-1.el8_6
    fixed: vendor fix RHSA-2025:8594
  • Red Hat Enterprise Linux AppStream TUS (v.8.8) thunderbird 128.10.1-1.el8_8
    fixed: vendor fix RHSA-2025:8784

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

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
last yr.

Exploit prediction

0.47% chance of exploitation in the next 30 days, higher than 40% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CISA ADP 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
CNA 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

Affected products

  • Mozilla Thunderbird

Classification

Weakness
  • CWE-356 Missing User Interaction for Potentially Unsafe Action

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.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.