CVE-2011-2609 in Web Browser
Summary
by MITRE
Opera before 11.50 does not properly restrict data: URIs, which makes it easier for remote attackers to conduct cross-site scripting (XSS) attacks via a crafted web site.
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Analysis
by VulDB Data Team • 11/13/2021
The vulnerability identified as CVE-2011-2609 represents a critical security flaw in Opera web browsers prior to version 11.50, specifically concerning the improper handling of data: URIs within the browser's security model. This weakness stems from the browser's insufficient validation mechanisms that govern how data URIs are processed and rendered, creating a pathway for malicious actors to exploit the browser's trust model. Data URIs are a method of embedding small data files directly into web pages using base64 encoding or other formats, typically intended for legitimate purposes such as inline images or small scripts. However, when improperly restricted, these URIs can be leveraged to execute malicious code within the context of the user's browsing session.
The technical flaw manifests when Opera's security architecture fails to adequately sanitize or validate data: URIs that are embedded within web pages or passed through user interactions. This allows attackers to craft malicious websites that include data URIs containing JavaScript or other executable content, which the browser then processes without proper security boundaries. The vulnerability operates at the intersection of browser security policies and URI handling mechanisms, where the expected sandboxing of data URIs is bypassed. This flaw is categorized under CWE-20, "Improper Input Validation," as it represents a failure to properly validate the content and origin of data URIs before executing them within the browser's security context.
The operational impact of this vulnerability is significant as it enables remote attackers to conduct cross-site scripting attacks with minimal user interaction. An attacker can construct a malicious website that includes a data URI pointing to a crafted payload, which when loaded in an affected Opera browser, executes within the context of the user's session. This creates a persistent threat vector that can be exploited across multiple websites, as the browser's trust model is manipulated to allow execution of potentially malicious code from data URIs. The vulnerability is particularly dangerous because it can be exploited without requiring any special privileges or user consent, making it a prime target for drive-by download attacks and social engineering campaigns.
The exploitability of this vulnerability aligns with techniques described in the attack pattern taxonomy under ATT&CK framework, specifically related to initial access and execution phases. Attackers can leverage this weakness through various delivery mechanisms including phishing emails, compromised websites, or malicious advertisements that redirect users to crafted pages. The vulnerability creates a persistent threat vector that can be used to establish command and control channels, steal session cookies, or perform other malicious activities within the user's browser context. Organizations and users are particularly vulnerable when browsing untrusted websites or when encountering malicious content that exploits this specific weakness in Opera's URI handling implementation.
Mitigation strategies for CVE-2011-2609 primarily focus on immediate browser updates to version 11.50 or later, where Opera implemented proper restrictions on data: URI processing. Security administrators should also consider implementing additional protective measures such as content filtering systems, web application firewalls, and browser security policies that restrict data URI execution. Network-level protections can include blocking or monitoring data URI traffic patterns, while user education programs should emphasize the importance of keeping browsers updated and avoiding suspicious websites. The vulnerability serves as a reminder of the critical importance of proper URI validation and the need for robust security boundaries within browser implementations, particularly as web technologies continue to evolve with more complex data handling mechanisms.