CVE-2025-5020

Opening maliciously-crafted URLs in Firefox from other apps such as Safari could have allowed attackers to spoof website addresses if the URLs utilized non-HTTP schemes used internally by the Firefox iOS client This vulnerability affects Firefox for iOS < 139.

Weakness

The product uses a handler for a custom URL scheme, but it does not properly restrict which actors can invoke the handler using the scheme.

Affected Software

Potential Mitigations

• Utilize a user prompt pop-up to authorize potentially harmful actions such as those modifying data or dealing with sensitive information.
• When designing functionality of actions in the URL scheme, consider whether the action should be accessible to all mobile applications, or if an allowlist of applications to interface with is appropriate.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1951558
• https://www.mozilla.org/security/advisories/mfsa2025-39/