CVE-2025-39098.1HighCWE-356

CVE-2025-3909: JavaScript Execution via Spoofed PDF Attachment and file:/// Link

Mozilla · Thunderbird

Vendor fix available · Affected: Mozilla Thunderbird · Exploitation: unlikely (under 1%)

Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.

0.5%probability of exploitation in the next 30 days

41st percentile

050100

Higher than 41% of scored CVEs

8.1HighCVSS 3.1

LowMediumHighCrit.

DescriptionCVE.org

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.

Affected products1

From the CVE record. A product or version that is not listed is unknown, not unaffected.

Mozilla · ThunderbirdVersions not stated

On the Atlas

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Open the Atlas

Exploitation: Unlikely (under 1%). EPSS under 1%, or no score yet.
CISA KEV: Not listed
Public check: No public nuclei template
Weakness: Missing User Interaction for Potentially Unsafe Action · Access Control
Vendor: Mozilla
Published: May 2025
Band: Unlikely (under 1%), May 2025

CoverageNo articles yet

No CyberSIXT article names CVE-2025-3909 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.