CVE-2011-4681 in Web Browser
Summary
by MITRE
Opera before 11.60 does not properly consider the number of . (dot) characters that conventionally exist in domain names of different top-level domains, which allows remote attackers to bypass the Same Origin Policy by leveraging access to a different domain name in the same top-level domain, as demonstrated by the .no or .uk domain.
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Analysis
by VulDB Data Team • 11/27/2021
The vulnerability described in CVE-2011-4681 represents a critical flaw in Opera browser's implementation of the Same Origin Policy mechanism, which serves as a fundamental security boundary in web applications. This weakness specifically affects Opera versions prior to 11.60 and stems from an inadequate handling of domain name validation logic that fails to properly account for the conventional number of dot characters present in various top-level domains. The Same Origin Policy is a core security principle that prevents scripts from one origin from accessing resources of another origin, thereby protecting users from cross-site scripting attacks and other malicious activities. When this policy is improperly implemented, it creates exploitable conditions that allow attackers to bypass these essential security controls.
The technical flaw manifests in Opera's domain validation process where the browser fails to correctly interpret the standard domain name structure across different top-level domains such as .no (Norway) and .uk (United Kingdom). This implementation error occurs because the browser's security model does not properly distinguish between legitimate domain boundaries and potentially deceptive domain structures that might appear similar but belong to different top-level domains. The vulnerability exploits the fact that certain TLDs follow conventional naming patterns with specific numbers of dots, and Opera's flawed validation logic allows attackers to craft domain names that appear to belong to a different domain but actually exploit the browser's insufficient validation mechanisms. This misinterpretation enables attackers to construct malicious URLs or web content that can bypass the security checks designed to prevent cross-origin access.
The operational impact of this vulnerability is significant as it allows remote attackers to perform cross-origin resource access attacks that would normally be blocked by proper Same Origin Policy enforcement. Attackers can leverage this weakness to access resources or data from different domains within the same top-level domain, potentially enabling them to steal session cookies, access sensitive information, or perform unauthorized actions on behalf of users. The attack vector specifically targets the .no and .uk domain examples, indicating that the vulnerability affects how Opera handles domain name parsing for these particular top-level domains. This weakness essentially allows for a form of domain-based cross-site scripting where an attacker can exploit the browser's inconsistent handling of domain boundaries to gain unauthorized access to resources that should remain protected by the Same Origin Policy.
This vulnerability aligns with CWE-284, which describes improper access control mechanisms, and represents a failure in proper security boundary enforcement within the browser's security architecture. The issue also maps to ATT&CK technique T1071.001, which covers application layer protocol usage for command and control communications, as the bypassed security controls could potentially be used for establishing unauthorized access channels. Organizations using affected Opera versions face increased risk of data breaches and unauthorized access to sensitive web applications, particularly those handling user authentication or confidential information. The vulnerability demonstrates how seemingly minor implementation flaws in security-critical components can create substantial risks that require immediate remediation through browser updates.
The recommended mitigation involves upgrading to Opera version 11.60 or later, which contains the necessary fixes for proper domain validation and Same Origin Policy enforcement. System administrators should also implement additional monitoring for suspicious domain access patterns and consider implementing web application firewalls that can detect and block potentially malicious cross-origin access attempts. Security teams should conduct thorough testing to ensure that the updated browser versions properly enforce security boundaries and that no other similar domain validation issues exist within the browser's security model. Organizations should also review their web application security configurations to ensure that additional defensive measures are in place to protect against potential exploitation of this vulnerability.