CVE - CVE-2025-3909

CVE-ID
CVE-2025-3909	Learn more at National Vulnerability Database (NVD) • CVSS Severity Rating • Fix Information • Vulnerable Software Versions • SCAP Mappings • CPE Information
Description
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 affects Thunderbird < 128.10.1 and Thunderbird < 138.0.1.
References
Note: References are provided for the convenience of the reader to help distinguish between vulnerabilities. The list is not intended to be complete.
MISC:https://bugzilla.mozilla.org/show_bug.cgi?id=1958376 URL:https://bugzilla.mozilla.org/show_bug.cgi?id=1958376 MISC:https://www.mozilla.org/security/advisories/mfsa2025-34/ URL:https://www.mozilla.org/security/advisories/mfsa2025-34/ MISC:https://www.mozilla.org/security/advisories/mfsa2025-35/ URL:https://www.mozilla.org/security/advisories/mfsa2025-35/
Assigning CNA
Mozilla Corporation
Date Record Created
20250423	Disclaimer: The record creation date may reflect when the CVE ID was allocated or reserved, and does not necessarily indicate when this vulnerability was discovered, shared with the affected vendor, publicly disclosed, or updated in CVE.
Phase (Legacy)
Assigned (20250423)
Votes (Legacy)

Comments (Legacy)

Proposed (Legacy)
N/A
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