Mozilla Firefox up to 138 on iOS URL improper authorization in handler for custom url scheme

Summaryinfo

A vulnerability identified as problematic has been detected in Mozilla Firefox up to 138 on iOS. This affects an unknown part of the component URL Handler. Performing a manipulation results in improper authorization in handler for custom url scheme. This vulnerability is reported as CVE-2025-5020. The attack is possible to be carried out remotely. No exploit exists. You should upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, was found in Mozilla Firefox up to 138 on iOS. This affects some unknown functionality of the component URL Handler. The manipulation with an unknown input leads to a improper authorization in handler for custom url scheme vulnerability. CWE is classifying the issue as CWE-939. 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. This is going to have an impact on integrity. The summary by CVE is:

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.

It is possible to read the advisory at bugzilla.mozilla.org. This vulnerability is uniquely identified as CVE-2025-5020 since 05/21/2025. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 06/13/2025).

Upgrading to version 139 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2025-16036). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Type

• Web Browser

Vendor

• Mozilla

Name

• Firefox

Version

• 138

License

• open-source

Website

• Vendor: https://www.mozilla.org/
• Product: https://www.mozilla.org/en-US/firefox/

CPE 2.3info

• 🔍

CPE 2.2info

• 🔍

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Be aware that VulDB is the high quality source for vulnerability data.

Discussion