CVE-2016-5268 in Firefox
Summary
by MITRE
Mozilla Firefox before 48.0 does not properly set the LINKABLE and URI_SAFE_FOR_UNTRUSTED_CONTENT flags of about: URLs that are used for error pages, which makes it easier for remote attackers to conduct spoofing attacks via a crafted URL, as demonstrated by misleading text after an about:neterror?d= substring.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 10/09/2024
The vulnerability identified as CVE-2016-5268 affects Mozilla Firefox versions prior to 48.0 and represents a significant security flaw in the browser's handling of about: URLs used for error pages. This issue stems from improper configuration of critical security flags that govern how these special URLs are processed and displayed within the browser environment. The flaw specifically impacts the LINKABLE and URI_SAFE_FOR_UNTRUSTED_CONTENT flags, which are essential components in Firefox's security architecture for managing privileged content access.
The technical implementation of this vulnerability involves the browser's failure to correctly set security attributes for about: URLs that serve as error page placeholders. When Firefox encounters an error condition such as network failures or security issues, it typically displays a specialized error page using about: URLs. However, in vulnerable versions, these URLs do not properly enforce the security restrictions that should prevent them from being used in malicious contexts. The LINKABLE flag controls whether a URL can be used as a hyperlink target, while the URI_SAFE_FOR_UNTRUSTED_CONTENT flag determines whether a URL can safely be displayed in contexts where untrusted content might be present. When these flags are improperly set, attackers can exploit the inconsistency to craft malicious URLs that appear legitimate while actually containing deceptive content.
The operational impact of this vulnerability enables sophisticated spoofing attacks where remote attackers can manipulate the display of error pages to mislead users about the true nature of their browsing activity. The demonstration of this flaw involved creating a crafted URL with the about:neterror?d= substring that could present misleading text to users, effectively allowing attackers to impersonate legitimate web resources. This type of attack falls under the broader category of phishing and user deception techniques that can compromise user trust and potentially lead to credential theft or other malicious activities. The vulnerability essentially undermines Firefox's security model by allowing untrusted content to be rendered in contexts where such behavior should be strictly prohibited.
From a cybersecurity perspective, this vulnerability aligns with CWE-611 Improper Restriction of XML External Entity Reference, as it involves improper handling of external references within privileged contexts. The attack vector demonstrates characteristics consistent with ATT&CK technique T1566.001 Phishing, where attackers exploit browser security flaws to create convincing deceptive interfaces. The vulnerability also relates to CWE-20 Improper Input Validation, since the browser fails to properly validate and restrict the behavior of about: URLs when they are used in error page contexts. Organizations and users should immediately update to Firefox 48.0 or later versions to remediate this vulnerability, as the fix ensures proper enforcement of security flags for about: URLs. Additionally, network administrators should monitor for potential exploitation attempts and consider implementing additional browser hardening measures. The vulnerability serves as a reminder of the critical importance of proper privilege separation in browser security architectures and the need for comprehensive testing of security features that govern how special URLs are handled within web browsers.
The remediation process requires updating Firefox installations to version 48.0 or higher, which includes proper implementation of the LINKABLE and URI_SAFE_FOR_UNTRUSTED_CONTENT flags for about: URLs. Security teams should also consider implementing browser security policies that further restrict the behavior of privileged URLs and monitor for any attempts to exploit similar vulnerabilities in other browser components. Organizations that cannot immediately update should consider implementing network-level protections such as content filtering and URL reputation services to mitigate the risk of exploitation.