CVE-2025-3877: Infoleak
A crafted HTML email using mailbox:/// links can trigger automatic, unsolicited downloads of .pdf files to the user's desktop or home directory without prompting, even if auto-saving is disabled. This behavior can be abused to fill the disk with garbage data (e.g. using /dev/urandom on Linux) or to leak Windows credentials via SMB links when the email is viewed in HTML mode. While user interaction is required to download the .pdf file, visual obfuscation can conceal the download trigger. Viewing the email in HTML mode is enough to load external content.
Other sources
Rejected reason: This CVE was marked as fixed, but due to other code landing - was not actually fixed. It was subsequently fixed in CVE-2025-5986.
— NVD
Affected Software
Event History
Peer vulnerabilities
Found alongside the following vulnerabilities.
Frequently Asked Questions
What is the severity of CVE-2025-3877?
CVE-2025-3877 has a high severity rating due to its potential to trigger unsolicited downloads of files.
How do I fix CVE-2025-3877?
To mitigate CVE-2025-3877, update Mozilla Thunderbird to version 138.0.1 or later.
What versions of Thunderbird are affected by CVE-2025-3877?
CVE-2025-3877 affects Thunderbird versions below 128.10.1 and 138.0.1.
What kind of files can be downloaded due to CVE-2025-3877?
CVE-2025-3877 can lead to automatic downloads of .pdf files without user consent.
Can CVE-2025-3877 be exploited remotely?
Yes, CVE-2025-3877 can be exploited remotely through crafted HTML emails.