CVE-2007-0996 in Firefox
Summary
by MITRE
The child frames in Mozilla Firefox before 1.5.0.10 and 2.x before 2.0.0.2, and SeaMonkey before 1.0.8 inherit the default charset from the parent window, which allows remote attackers to conduct cross-site scripting (XSS) attacks, as demonstrated using the UTF-7 character set.
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Analysis
by VulDB Data Team • 07/13/2021
This vulnerability resides in the browser engine's handling of character encoding within nested frame structures, specifically affecting Mozilla Firefox versions prior to 1.5.0.10 and 2.x versions prior to 2.0.0.2, along with SeaMonkey versions before 1.0.8. The core issue stems from how child frames inherit the default character set from their parent window, creating a potential security gap that can be exploited by malicious actors. When a parent window is configured to use a specific character encoding, child frames automatically adopt this same encoding without proper validation or isolation, leading to unexpected behavior in how content is interpreted and rendered.
The technical flaw manifests through the improper inheritance of character encoding settings between parent and child frames, creating a scenario where attackers can manipulate the encoding context to bypass security restrictions. This particular vulnerability was demonstrated using the UTF-7 character set, which has historically been problematic in web security contexts due to its ability to encode arbitrary data in a way that can be interpreted as HTML or script content. The inheritance mechanism allows malicious content in a child frame to be interpreted using the parent's character encoding, potentially enabling attackers to inject malicious scripts that would otherwise be blocked by proper encoding validation.
The operational impact of this vulnerability is significant for web application security, as it allows remote attackers to conduct cross-site scripting attacks by leveraging the encoding inheritance behavior. An attacker could craft content that appears benign when interpreted under one encoding but becomes malicious when interpreted under the inherited encoding from the parent window. This creates a vector for injecting script code that can execute within the context of the parent window, potentially leading to session hijacking, data theft, or other malicious activities. The vulnerability essentially weakens the security boundaries between frames, allowing content from one frame to influence the interpretation of content in another frame.
This vulnerability aligns with CWE-1004 which addresses insecure default conditions, and represents a specific instance of improper handling of character encoding in web browsers. From an ATT&CK perspective, this maps to techniques involving command and control through web browsers, specifically leveraging browser security weaknesses to execute malicious code. The issue also relates to privilege escalation through browser-based attacks, as the inherited encoding can allow attackers to bypass security mechanisms that would normally prevent script execution. The mitigation strategy involves implementing proper isolation of character encoding contexts between parent and child frames, ensuring that each frame maintains its own encoding settings rather than inheriting from the parent. This typically requires updating the browser to a patched version that properly handles encoding inheritance or implementing additional security measures such as content security policies that restrict frame behavior and encoding inheritance.