Mozilla Foundation Security Advisory 2025-54
Security Vulnerabilities fixed in Thunderbird 140
- Announced
- July 2, 2025
- Impact
- high
- Products
- Thunderbird
- Fixed in
-
- Thunderbird 140
In general, these flaws cannot be exploited through email in the Thunderbird product because scripting is disabled when reading mail, but are potentially risks in browser or browser-like contexts.
#CVE-2025-6424: Use-after-free in FontFaceSet
- Reporter
- LJP and HexRabbit (DEVCORE Research Team)
- Impact
- high
Description
A use-after-free in FontFaceSet resulted in a potentially exploitable crash.
References
#CVE-2025-6425: The WebCompat WebExtension shipped exposed a persistent UUID
- Reporter
- Rob Wu
- Impact
- moderate
Description
An attacker who enumerated resources from the WebCompat extension could have obtained a persistent UUID that identified the browser, and persisted between containers and normal/private browsing mode, but not profiles.
References
#CVE-2025-6426: No warning when opening executable terminal files on macOS
- Reporter
- pwn2car
- Impact
- moderate
Description
The executable file warning did not warn users before opening files with the terminal extension.
This bug only affects Thunderbird for macOS. Other versions of Thunderbird are unaffected.
References
#CVE-2025-6427: connect-src Content Security Policy restriction could be bypassed
- Reporter
- Alan Li (lebr0nli)
- Impact
- moderate
Description
An attacker was able to bypass the connect-src directive of a Content Security Policy by manipulating subdocuments. This would have also hidden the connections from the Network tab in Devtools.
References
#CVE-2025-6429: Incorrect parsing of URLs could have allowed embedding of youtube.com
- Reporter
- Masato Kinugawa
- Impact
- moderate
Description
Thunderbird could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in an embed tag. This could have bypassed website security checks that restricted which domains users were allowed to embed.
References
#CVE-2025-6430: Content-Disposition header ignored when a file is included in an embed or object tag
- Reporter
- Daniil Satyaev (Positive Technologies)
- Impact
- moderate
Description
When a file download is specified via the Content-Disposition header, that directive would be ignored if the file was included via a <embed> or <object> tag, potentially making a website vulnerable to a cross-site scripting attack.
References
#CVE-2025-6432: DNS Requests leaked outside of a configured SOCKS proxy
- Reporter
- Albert
- Impact
- low
Description
When Multi-Account Containers was enabled, DNS requests could have bypassed a SOCKS proxy when the domain name was invalid or the SOCKS proxy was not responding.
References
#CVE-2025-6433: WebAuthn would allow a user to sign a challenge on a webpage with an invalid TLS certificate
- Reporter
- Simon
- Impact
- low
Description
If a user visited a webpage with an invalid TLS certificate, and granted an exception, the webpage was able to provide a WebAuthn challenge that the user would be prompted to complete. This is in violation of the WebAuthN spec which requires "a secure transport established without errors".
References
#CVE-2025-6434: HTTPS-Only exception screen lacked anti-clickjacking delay
- Reporter
- hafiizh & kang ali
- Impact
- low
Description
The exception page for the HTTPS-Only feature, displayed when a website is opened via HTTP, lacked an anti-clickjacking delay, potentially allowing an attacker to trick a user into granting an exception and loading a webpage over HTTP.
References
#CVE-2025-6435: Save as in Devtools could download files without sanitizing the extension
- Reporter
- Ameen Basha M K
- Impact
- low
Description
If a user saved a response from the Network tab in Devtools using the Save As context menu option, that file may not have been saved with the .download file extension. This could have led to the user inadvertently running a malicious executable.
References
#CVE-2025-6436: Memory safety bugs fixed in Firefox 140 and Thunderbird 140
- Reporter
- Andrew McCreight, Gabriele Svelto, Beth Rennie (she/her), the Mozilla Fuzzing Team
- Impact
- high
Description
Memory safety bugs present in Firefox 139 and Thunderbird 139. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code.