CVE-2015-7211 in Firefox
Summary
by MITRE
Mozilla Firefox before 43.0 mishandles the # (number sign) character in a data: URI, which allows remote attackers to spoof web sites via unspecified vectors.
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Analysis
by VulDB Data Team • 07/01/2022
The vulnerability identified as CVE-2015-7211 represents a significant security flaw in Mozilla Firefox versions prior to 43.0 that relates to improper handling of the hash character within data URIs. This issue stems from how the browser processes data URIs that contain the # character, creating a potential avenue for malicious actors to manipulate web content presentation and deceive users about the true origin of web pages.
The technical flaw manifests in Firefox's URI parsing mechanism where the browser fails to properly normalize or sanitize data URIs containing the # character. When a data URI includes a hash symbol followed by additional content, the browser's interpretation of the URI structure becomes inconsistent with standard web security expectations. This inconsistency creates opportunities for attackers to craft malicious data URIs that appear to originate from trusted sources while actually containing different content or directing users to unintended destinations.
From an operational perspective, this vulnerability enables sophisticated phishing attacks and website spoofing techniques that can bypass traditional security measures. Attackers can leverage this flaw to create deceptive web page presentations where the URL bar displays a legitimate domain while the actual content rendered is controlled by malicious data URI content. The impact extends beyond simple deception as it can facilitate credential theft, malware distribution, and other malicious activities that rely on user trust in the displayed web address.
The vulnerability aligns with CWE-170, which addresses improper handling of null terminators or similar special characters in input processing, and relates to ATT&CK technique T1059.001 for command and scripting interpreter usage in phishing scenarios. Security researchers have documented that this issue can be exploited across multiple attack vectors including email phishing campaigns, compromised websites, and social engineering attacks that specifically target Firefox users.
Organizations should implement immediate mitigation strategies including mandatory browser updates to Firefox 43.0 or later versions, deployment of web application firewalls that can detect and block suspicious data URI patterns, and enhanced user education regarding URL verification practices. Network administrators should also consider implementing content filtering solutions that can identify and block potentially malicious data URI constructs. The vulnerability underscores the importance of proper URI normalization and input validation in web browser implementations, as highlighted in industry security best practices and standards such as those defined by the Open Web Application Security Project.