CVE-2016-5282 in Firefox
Summary
by MITRE
Mozilla Firefox before 49.0 does not properly restrict the scheme in favicon requests, which might allow remote attackers to obtain sensitive information via unspecified vectors, as demonstrated by a jar: URL for a favicon resource.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability identified as CVE-2016-5282 represents a significant information disclosure flaw in Mozilla Firefox versions prior to 49.0. This issue stems from inadequate validation of URL schemes in favicon request handling, creating potential attack vectors that could expose sensitive data to remote adversaries. The vulnerability specifically manifests when Firefox processes favicon requests through jar: URLs, which are typically used to access resources within Java archive files. The improper scheme restriction allows attackers to craft malicious favicon requests that could potentially bypass normal security boundaries and access resources that should remain protected.
The technical flaw resides in Firefox's handling of web resource requests, particularly when processing favicon URLs that reference jar: schemes. This vulnerability falls under the broader category of insecure direct object references and improper input validation as classified by CWE-284. The implementation fails to properly validate the scheme component of URLs before processing them as favicon resources, allowing arbitrary scheme specifications to be interpreted by the browser's resource loading mechanism. When a web page attempts to load a favicon using a jar: URL, Firefox should ideally restrict such requests to prevent access to local resources or unauthorized network locations, but the validation mechanism was insufficient to prevent this type of cross-scheme access.
The operational impact of this vulnerability extends beyond simple information disclosure, as it could enable attackers to construct sophisticated attacks leveraging the browser's resource loading behavior. An attacker could potentially craft web pages that attempt to load favicons from jar: URLs pointing to sensitive local resources or network locations that should not be accessible through normal browsing operations. This capability could be exploited to gather information about the victim's local system configuration, access internal network resources, or potentially escalate privileges within the browser sandbox. The vulnerability demonstrates how seemingly innocuous features like favicon handling can become attack vectors when proper input validation is lacking, as outlined in the ATT&CK framework's technique for privilege escalation through browser features.
Mitigation strategies for CVE-2016-5282 primarily focus on updating Firefox installations to version 49.0 or later, where the vulnerability has been addressed through enhanced URL scheme validation in favicon processing. Organizations should implement comprehensive patch management procedures to ensure all Firefox installations are updated promptly. Additionally, network administrators can deploy web application firewalls or proxy configurations that monitor and restrict jar: URL access patterns, though this approach provides only partial protection. The vulnerability highlights the importance of proper input validation and scheme restriction in web browser implementations, as recommended by security standards such as the OWASP Top Ten and NIST cybersecurity guidelines. Browser vendors should implement strict validation of URL components in resource loading contexts, particularly for features like favicons that are often overlooked in security reviews but can serve as attack vectors.