Vulnerability · Published Jun 11, 2025 · Assigned by mozilla
CVE-2025-5986Unsolicited File Download, Disk Space Exhaustion, and Credential Leakage via mailbox:/// Links
Medium 6.5
In plain English
A medium-severity security flaw in Thunderbird from Mozilla. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 48% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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. This vulnerability was fixed in Thunderbird 128.11.1 and Thunderbird 139.0.2.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | thunderbird | 128.12.0-1.el10_0.alma.1 | ALSA-2025:10195 |
| AlmaLinux:8 | thunderbird | 128.12.0-1.el8_10.alma.1 | ALSA-2025:10246 |
| AlmaLinux:9 | thunderbird | 128.12.0-1.el9_6.alma.1 | ALSA-2025:10196 |
| Debian:12 | thunderbird | 1:128.12.0esr-1~deb12u1 | DSA-5959-1 |
| Debian:12 | thunderbird | 1:128.12.0esr-1~deb12u1 | DEBIAN-CVE-2025-5986 |
| Debian:13 | thunderbird | 1:128.12.0esr-1 | DEBIAN-CVE-2025-5986 |
| Debian:14 | thunderbird | 1:128.12.0esr-1 | DEBIAN-CVE-2025-5986 |
| Rocky Linux:10 | thunderbird | 0:128.12.0-1.el10_0 | RLSA-2025:10195 |
| Rocky Linux:8 | thunderbird | 0:128.12.0-1.el8_10 | RLSA-2025:10246 |
| Rocky Linux:9 | thunderbird | 0:128.12.0-1.el9_6 | RLSA-2025:10196 |
| Ubuntu:22.04:LTS | thunderbird | 1:128.12.0+build1-0ubuntu0.22.04.1 | UBUNTU-CVE-2025-5986 |
| Ubuntu:22.04:LTS | thunderbird | 1:128.12.0+build1-0ubuntu0.22.04.1 | USN-7663-1 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Thunderbird | see references |
Weakness: CWE-451 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H