CVE-2016-5283 in Firefox
Summary
by MITRE
Mozilla Firefox before 49.0 allows remote attackers to bypass the Same Origin Policy via a crafted fragment identifier in the SRC attribute of an IFRAME element, leading to insufficient restrictions on link-color information after a document is resized.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability identified as CVE-2016-5283 represents a critical security flaw in Mozilla Firefox versions prior to 49.0 that undermines the fundamental Same Origin Policy mechanism. This policy serves as a cornerstone of web security by preventing scripts from one origin from accessing resources or data from another origin, thereby protecting users from cross-site scripting attacks and data leakage. The flaw specifically exploits the handling of fragment identifiers within iframe source attributes, creating a pathway for malicious actors to circumvent these essential security boundaries. The vulnerability manifests when a crafted fragment identifier is embedded in the src attribute of an iframe element, allowing attackers to manipulate how link colors are displayed after document resizing operations.
The technical implementation of this vulnerability stems from Firefox's insufficient validation of fragment identifiers when processing iframe elements. Fragment identifiers are typically used to reference specific sections within a document, but in this case, attackers can craft malicious fragment values that manipulate the browser's rendering engine to expose information that should remain restricted. When a document is resized, the browser's handling of these crafted identifiers causes it to improperly expose link color information that would normally be protected by the Same Origin Policy. This information leakage occurs because the fragment identifier manipulation bypasses normal security checks that would typically prevent cross-origin access to styling information.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables sophisticated attacks that can extract sensitive data through careful manipulation of document rendering. Attackers can leverage this flaw to gather information about the color schemes and styling properties of elements from different origins, potentially revealing patterns that could be used in more advanced attacks. The vulnerability particularly affects scenarios where users navigate to malicious websites that contain crafted iframes, and the subsequent document resizing triggers the information leakage. This makes it particularly dangerous in phishing attacks or social engineering campaigns where attackers can use the leaked information to craft more convincing deceptive interfaces.
Security researchers have classified this vulnerability under CWE-200, which deals with information exposure, and it aligns with ATT&CK technique T1056.001 for input validation and T1566.001 for credential access through social engineering. The flaw demonstrates the importance of comprehensive input validation in web browsers and highlights how seemingly innocuous fragment identifier handling can create significant security risks. Organizations should prioritize immediate patching of affected Firefox versions, as the vulnerability provides attackers with a means to bypass fundamental security protections that are essential for maintaining user privacy and data integrity. The fix implemented in Firefox 49.0 involved strengthening the validation of fragment identifiers within iframe attributes and ensuring that document resizing operations properly enforce cross-origin restrictions.
This vulnerability underscores the complexity of modern web security and the challenges inherent in maintaining robust protection mechanisms across diverse browser implementations. The attack vector demonstrates how sophisticated manipulation of standard web features can create unexpected security holes, emphasizing the need for continuous security auditing and the importance of maintaining up-to-date browser software. Organizations should implement comprehensive security awareness training to help users recognize potentially malicious websites and ensure that security patches are applied promptly across all systems. The incident also highlights the critical role of browser vendors in maintaining security through regular updates and the importance of adhering to established security standards and best practices in web application development.