CVE-2010-4043 in Web Browser
Summary
by MITRE
Opera before 10.63 does not prevent interpretation of a cross-origin document as a CSS stylesheet when the document lacks a CSS token sequence, which allows remote attackers to obtain sensitive information via a crafted document.
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Analysis
by VulDB Data Team • 09/28/2021
The vulnerability described in CVE-2010-4043 represents a critical cross-origin resource handling flaw in Opera web browsers prior to version 10.63. This issue stems from the browser's insufficient validation mechanisms when processing cross-origin documents that are intended to be interpreted as CSS stylesheets. The vulnerability specifically manifests when a cross-origin document lacks proper CSS token sequences, creating an opportunity for malicious actors to exploit the browser's interpretation logic.
The technical flaw resides in Opera's document parsing and interpretation engine which fails to properly enforce cross-origin restrictions when processing CSS content. When a document is fetched from a different origin but is interpreted as a stylesheet, the browser should typically reject such content or enforce strict security boundaries. However, in affected versions, Opera's parser allows documents without CSS tokens to be processed as if they were legitimate CSS files, potentially exposing sensitive information through unintended data leakage mechanisms. This behavior violates fundamental web security principles and represents a failure in the browser's content security model.
The operational impact of this vulnerability is significant as it enables remote attackers to conduct information disclosure attacks through crafted cross-origin documents. Attackers can construct malicious content that appears to be CSS but lacks proper token sequences, allowing them to bypass normal security restrictions. This weakness could potentially expose session cookies, user credentials, or other sensitive data that should remain isolated between different origins. The vulnerability essentially creates a pathway for cross-site information leakage that undermines the browser's security sandbox and violates the same-origin policy that forms the foundation of web security.
The exploitability of this vulnerability aligns with attack patterns documented in the ATT&CK framework under the information gathering and credential access tactics. Specifically, it relates to techniques involving cross-site scripting and information disclosure through malformed content processing. From a CWE perspective, this vulnerability maps to CWE-200, which covers improper output neutralization for logs, and potentially CWE-346, which addresses improper verification of intended target. The weakness demonstrates a failure in input validation and output sanitization that allows malicious content to be processed with elevated privileges.
Mitigation strategies for this vulnerability require immediate browser updates to version 10.63 or later, where Opera implemented proper cross-origin restriction enforcement. Organizations should also implement content security policies that restrict cross-origin stylesheet loading and monitor for suspicious cross-origin resource requests. Network-level protections including web application firewalls and proxy configurations can help detect and block malicious cross-origin content attempts. Additionally, security awareness training for developers regarding proper content validation and the importance of maintaining strict cross-origin boundaries should be emphasized. The vulnerability serves as a reminder of the critical importance of proper input validation and the need for comprehensive security testing of content processing pipelines in web browsers.