CVE-2020-6827 in Firefox ESR
Summary
by MITRE
When following a link that opened an intent://-schemed URL, causing a custom tab to be opened, Firefox for Android could be tricked into displaying the incorrect URI. <br> *Note: This issue only affects Firefox for Android. Other operating systems are unaffected.*. This vulnerability affects Firefox ESR < 68.7.
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Analysis
by VulDB Data Team • 05/06/2025
This vulnerability in Firefox for Android represents a significant security flaw related to intent scheme handling that could lead to phishing attacks and user deception. The issue specifically affects the browser's handling of intent://-schemed URLs which are commonly used to launch applications through Android's intent system. When users clicked on links that triggered these intent schemes, Firefox for Android would incorrectly display the URI in the custom tab interface, potentially showing a malicious or misleading URL instead of the actual destination. This behavior creates a dangerous user experience where the displayed URL does not match the actual application being launched, undermining the user's ability to verify the legitimacy of their navigation. The vulnerability stems from improper validation and display handling of intent scheme URLs within the browser's custom tab implementation, which is a critical component for maintaining user trust and security in mobile browsing environments.
The technical implementation flaw involves the browser's custom tab functionality failing to properly sanitize or validate the URI components when processing intent:// URLs. This allows attackers to craft malicious links that, when clicked, cause Firefox to display a deceptive URL while actually launching a different application or navigating to a malicious destination. The issue occurs specifically during the transition from web content to custom tab presentation, where the URI display logic does not adequately verify that the displayed URL matches the actual intent being executed. This type of vulnerability falls under CWE-20 Improper Input Validation, as the browser fails to properly validate the intent scheme parameters before presenting them to users. The flaw also relates to CWE-601 URL Redirection to Untrusted Site, since the browser's handling of these schemes could redirect users to malicious destinations while appearing to show legitimate URLs.
The operational impact of this vulnerability extends beyond simple user confusion to potentially enable sophisticated phishing attacks and social engineering campaigns. Mobile users who rely on Firefox for Android may be tricked into believing they are visiting legitimate websites while actually being directed to malicious applications or pages. Attackers could exploit this by creating links that display trusted domain names while actually launching malicious applications or redirecting to phishing pages that mimic legitimate services. The vulnerability affects Firefox ESR versions prior to 68.7, representing a critical security gap that could be exploited in real-world scenarios where users frequently click on links from emails, social media, or other sources. This issue particularly impacts users who rely on Firefox for Android's custom tab functionality for secure browsing, as the browser's security model depends on users being able to verify the legitimacy of their navigation through accurate URL display.
Organizations and users should immediately upgrade to Firefox ESR 68.7 or later versions to address this vulnerability, as the flaw remains unpatched in older releases. The mitigation strategy involves not only updating the browser but also educating users about the importance of verifying URLs even when they appear to be displayed correctly in the browser interface. Security teams should monitor for exploitation attempts targeting this specific vulnerability in mobile environments, as it could be leveraged in targeted attacks against users who regularly use Firefox for Android. Additionally, the vulnerability highlights the importance of proper input validation in mobile browser implementations, particularly for handling Android-specific intent schemes that bridge web and application contexts. Organizations should also consider implementing additional security measures such as URL filtering and user education programs to reduce the risk of successful exploitation, as this type of vulnerability demonstrates how seemingly minor implementation flaws can create significant security risks in mobile browsing environments. The ATT&CK framework categorizes this vulnerability under T1566 Phishing and T1071.004 Application Layer Protocol: DNS, as it enables attackers to manipulate user perception through deceptive URL display while maintaining access to legitimate application launch mechanisms.