CVE-2025-5020 is a medium-severity vulnerability affecting Mozilla Firefox for iOS versions prior to 139. The issue arises when Firefox for iOS opens links using non-HTTP schemes that are invoked from other applications such as Safari. Specifically, maliciously crafted URLs leveraging internal non-HTTP schemes used by Firefox iOS could allow an attacker to spoof website addresses displayed within Firefox. This spoofing could mislead users into believing they are visiting a legitimate website when in fact they are interacting with a malicious or fraudulent site. The vulnerability is classified under CWE-939, which relates to improper control of a resource through its lifetime, indicating that the handling of these non-HTTP scheme URLs is not properly validated or sanitized. The CVSS 3.1 base score is 4.3, reflecting a medium impact primarily due to the lack of confidentiality impact but with some integrity concerns and no availability impact. Exploitation requires no privileges but does require user interaction (clicking a crafted link). The scope remains unchanged as the vulnerability affects only the Firefox for iOS client. No known exploits are currently reported in the wild, and no patches or mitigation links have been provided yet. This vulnerability could be leveraged in phishing or social engineering attacks to trick users into divulging sensitive information or credentials by impersonating trusted websites within the Firefox iOS browser environment.

For European organizations, the primary risk lies in targeted phishing campaigns exploiting this vulnerability to deceive users into visiting spoofed websites that appear legitimate within Firefox for iOS. This could lead to credential theft, unauthorized access to corporate resources, or distribution of malware. Since Firefox for iOS is used by a segment of mobile users, including employees accessing corporate resources remotely, the vulnerability could undermine trust in secure communications and increase the risk of data breaches. The lack of confidentiality impact reduces the risk of direct data leakage through the vulnerability itself, but the integrity impact could facilitate further attacks that compromise organizational security. The vulnerability's reliance on user interaction means that awareness and user training remain critical. Additionally, sectors with high reliance on mobile browsing for sensitive transactions, such as finance, healthcare, and government, may face elevated risks. Given the medium severity and the absence of known exploits, the immediate threat level is moderate but warrants prompt attention to prevent exploitation in targeted attacks.

1. Update Firefox for iOS to version 139 or later as soon as the patch becomes available to remediate the vulnerability. 2. Until a patch is released, organizations should consider restricting or monitoring the use of Firefox for iOS on corporate-managed devices, especially for high-risk user groups. 3. Implement mobile device management (MDM) policies to enforce browser updates and control app installations. 4. Educate users about the risks of clicking on links from untrusted sources, particularly those opened from other apps like Safari, and encourage verification of URLs before entering sensitive information. 5. Employ network-level protections such as DNS filtering and web proxy solutions that can detect and block access to known malicious domains or suspicious URLs. 6. Monitor for phishing campaigns targeting employees that may leverage this vulnerability and enhance email filtering rules accordingly. 7. Encourage the use of multi-factor authentication (MFA) to reduce the impact of credential compromise resulting from spoofing attacks. 8. Coordinate with Mozilla security advisories to stay informed about patch releases and further technical details.