Cyber Resilience

CVE-2025-3909

Mozilla Thunderbird ≤ 128.10.1

Published
14 May 2025
Modified
17 June 2026
Patch / advisory
View advisory
CVSS Score v3.1 8.1
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
EPSS Score 0.0041 34th percentile
Risk Priority 60 floored blend · peak EPSS

Summary

CVE-2025-3909 is a high-severity Product UI does not Warn User of Unsafe Actions (CWE-356) vulnerability in Mozilla Thunderbird. Its CVSS base score is 8.1 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique User Execution (T1204); ranked at the 34th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

EU & UK References

Vulnerability Data

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…

more

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.

CWE(s)
CWE-356

Related Threats

MITRE ATT&CK Enterprise Techniques

T1204 User Execution Execution
An adversary may rely upon specific actions by a user in order to gain execution.
attack.mitre.org →
T1204.001 Malicious Link Execution
An adversary may rely upon a user clicking a malicious link in order to gain execution.
attack.mitre.org →
T1204.002 Malicious File Execution
An adversary may rely upon a user opening a malicious file in order to gain execution.
attack.mitre.org →
T1204.004 Malicious Copy and Paste Execution
An adversary may rely upon a user copying and pasting code in order to gain execution.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-3889Same product: Mozilla Thunderbird
CVE-2025-3932Same product: Mozilla Thunderbird
CVE-2025-5262Same product: Mozilla Thunderbird
CVE-2025-26695Same product: Mozilla Thunderbird
CVE-2025-3523Same product: Mozilla Thunderbird
CVE-2026-57963Same product: Mozilla Thunderbird
CVE-2025-0510Same product: Mozilla Thunderbird
CVE-2026-4371Same product: Mozilla Thunderbird
CVE-2026-57962Same product: Mozilla Thunderbird
CVE-2025-3875Same product: Mozilla Thunderbird

Affected Assets

mozilla
thunderbird
≤ 128.10.1 · 129.0 — 138.0.1

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 1 hardening rule · 1 OS baseline
Validate
Prove the fix (OWASP ASVS)

—

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

SC-15 Collaborative Computing Devices and Applications
addresses: CWE-356

Mandates explicit user-visible indication, directly countering absence of warnings for device activation.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices include UI design requirements that warn users before unsafe actions.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can verify presence of warnings for unsafe user actions.

A.6.3 Information security awareness, education and training partial match
prevents

Security awareness training can teach users to heed or demand warnings for unsafe actions.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle requires UI design to warn users before unsafe actions.

A.8.26 Application security requirements partial match
prevents

Application security requirements include user warnings for dangerous operations.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles can mandate confirmation prompts for risky actions.

A.8.28 Secure coding partial match
prevents

Secure coding practices can embed user warnings before unsafe operations.

References