JavaScript Execution via Spoofed PDF Attachment and file:/// Link
Priority LOW 38CWE-356Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- Required
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- High · High · None
- Fix status
- Partial Red Hat: 13 fixed, 3 without a fix
Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA and Red Hat.
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.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.0047 40th percentileScored 2026-11-07
Fix Partial Thunderbird (Mozilla): 128.10.1, 138.0.1Red Hat: 10 advisoriesRed Hat: 13 fixed, 3 without a fix
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
Remediation
- Fix · CNA Thunderbird (Mozilla) Fixed in 128.10.1, 138.0.1
Red Hat 10 advisories
- RHSA-2025:8784 Released 2025-06-10 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux AppStream E4S (v.8.8) thunderbird-128.10.1-1.el8_8
- Red Hat Enterprise Linux AppStream TUS (v.8.8) thunderbird-128.10.1-1.el8_8
- RHSA-2025:8756 Released 2025-06-10 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux AppStream (v. 8) thunderbird-128.11.0-1.el8_10
- RHSA-2025:8594 Released 2025-06-05 · Red Hat rating Importantthunderbird security update
- 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
- Red Hat Enterprise Linux AppStream TUS (v.8.6) thunderbird-128.10.1-1.el8_6
Show 7 more Red Hat advisories
- RHSA-2025:8507 Released 2025-06-04 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux AppStream AUS (v.8.4) thunderbird-128.10.1-1.el8_4
- RHSA-2025:8391 Released 2025-06-02 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux AppStream AUS (v. 8.2) thunderbird-128.10.1-1.el8_2
- RHSA-2025:8325 Released 2025-05-29 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux AppStream EUS (v.9.4) thunderbird-128.10.1-1.el9_4
- RHSA-2025:8324 Released 2025-05-29 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux AppStream E4S (v.9.0) thunderbird-128.10.1-1.el9_0
- RHSA-2025:8326 Released 2025-05-29 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux AppStream EUS (v.9.2) thunderbird-128.10.1-1.el9_2
- RHSA-2025:8203 Released 2025-05-27 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux AppStream (v. 9) thunderbird-128.10.1-1.el9_6
- RHSA-2025:8196 Released 2025-05-27 · Red Hat rating Importantthunderbird security update
- Red Hat Enterprise Linux AppStream (v. 10) thunderbird-128.10.1-1.el10_0
Vendor assessments
Red Hat
Red Hat rating: Important. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 10 | Affected | No fix yet |
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 7 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux AppStream (v. 10) | Fixed | RHSA-2025:8196 |
| Red Hat Enterprise Linux AppStream (v. 8) | Fixed | RHSA-2025:8756 |
| Red Hat Enterprise Linux AppStream (v. 9) | Fixed | RHSA-2025:8203 |
| Red Hat Enterprise Linux AppStream AUS (v. 8.2) | Fixed | RHSA-2025:8391 |
| Red Hat Enterprise Linux AppStream AUS (v.8.4) | Fixed | RHSA-2025:8507 |
| Red Hat Enterprise Linux AppStream AUS (v.8.6) | Fixed | RHSA-2025:8594 |
| Red Hat Enterprise Linux AppStream E4S (v.8.6) | Fixed | RHSA-2025:8594 |
| Red Hat Enterprise Linux AppStream E4S (v.8.8) | Fixed | RHSA-2025:8784 |
| Red Hat Enterprise Linux AppStream E4S (v.9.0) | Fixed | RHSA-2025:8324 |
| Red Hat Enterprise Linux AppStream EUS (v.9.2) | Fixed | RHSA-2025:8326 |
| Red Hat Enterprise Linux AppStream EUS (v.9.4) | Fixed | RHSA-2025:8325 |
| Red Hat Enterprise Linux AppStream TUS (v.8.6) | Fixed | RHSA-2025:8594 |
| Red Hat Enterprise Linux AppStream TUS (v.8.8) | Fixed | RHSA-2025:8784 |
Timeline
- 2026-10-02 Threatist record created from CVE-2025-3909
- 2026-10-03 Alias added: GHSA-h6cg-6m9j-xj9g
References
More Mozilla Thunderbird vulnerabilities
- TI-2024-08981 Use after free in Mozilla Firefox KEVCVSS 3.1CRITICAL 9.8
- TI-2022-09832 Use after free in Mozilla Firefox KEVCVSS 3.1CRITICAL 9.6
- TI-2019-08769 Improper input validation in Mozilla Firefox ESR KEVCVSS 3.1CRITICAL 10.0
- TI-2010-03577 Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before… KEVCVSS 3.1CRITICAL 9.8
- TI-2023-04799 Out-of-bounds write in Google Chrome KEVCVSS 3.1HIGH 8.8
- TI-2023-04477 Out-of-bounds write in Google Chrome KEVCVSS 3.1HIGH 8.8
Sources
- CVE-2025-3909 · CVE Program
- CVE-2025-3909 · NVD
- FIRST EPSS
- GHSA-h6cg-6m9j-xj9g · GitHub Advisory Database · CC BY 4.0
- CVE-2025-3909 · Red Hat security data · CC BY 4.0
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