CVE-2008-5681 in Web Browser
Summary
by MITRE
Opera before 9.63 does not block unspecified "scripted URLs" during the feed preview, which allows remote attackers to read existing subscriptions and force subscriptions to arbitrary feed URLs.
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Analysis
by VulDB Data Team • 08/23/2019
The vulnerability identified as CVE-2008-5681 affects Opera web browsers version 9.62 and earlier, representing a significant security flaw in the browser's handling of feed preview functionality. This issue stems from the browser's failure to properly validate and sanitize URL schemes during the feed preview process, creating an avenue for malicious actors to exploit the system's trust model. The vulnerability specifically targets the feed preview feature that allows users to view RSS or Atom feed content before subscribing to it, which is a common and expected functionality in modern web browsers.
The technical flaw manifests in Opera's inadequate filtering of what are termed "scripted URLs" during feed preview operations. Scripted URLs typically include protocols such as javascript:, vbscript:, or other potentially dangerous schemes that could execute code when processed by a browser. The vulnerability occurs because Opera's feed preview mechanism does not sufficiently block these unspecified URL schemes, allowing them to be processed and executed within the preview context. This design oversight creates a scenario where an attacker can craft malicious feed entries containing these dangerous URLs, which will be executed when the user previews the feed content.
The operational impact of this vulnerability is substantial as it enables remote attackers to perform two distinct malicious activities through a single exploit vector. First, attackers can read existing subscriptions by leveraging the feed preview functionality to extract information about currently subscribed feeds, potentially exposing user interests and browsing habits. Second, attackers can force users to subscribe to arbitrary feed URLs, which could redirect them to malicious websites, deliver phishing content, or even install unwanted software through the feed subscription mechanism. This dual capability makes the vulnerability particularly dangerous as it provides both information disclosure and unauthorized action capabilities.
This vulnerability maps to CWE-174, which describes "Single Character Flaw in a String," specifically relating to improper handling of URL schemes during feed processing. The attack pattern aligns with techniques described in the MITRE ATT&CK framework under the T1059.007 sub-technique for "Command and Scripting Interpreter: JavaScript," where adversaries leverage browser-based scripting environments to execute malicious code. The vulnerability also demonstrates characteristics of T1566.001 for "Phishing: Spearphishing Attachment," as attackers could craft malicious feeds that appear legitimate but contain hidden malicious URLs.
The security implications extend beyond immediate exploitation as this vulnerability represents a failure in the browser's security model for handling potentially dangerous content. The feed preview feature, designed to be a safe browsing experience, becomes a vector for code execution due to insufficient input validation. Users who regularly interact with RSS feeds or atom feeds would be particularly vulnerable, as the attack requires only that they preview a malicious feed entry. The vulnerability also highlights the importance of proper protocol handling in web browsers, where the distinction between safe and dangerous URL schemes must be clearly enforced to prevent privilege escalation through seemingly benign user interactions.
Mitigation strategies for this vulnerability include immediate browser updates to Opera version 9.63 or later, which contain the necessary patches to properly filter scripted URLs during feed preview operations. System administrators should also implement feed filtering at the network level, particularly for environments where users may be exposed to untrusted feed sources. Additionally, user education about the risks of previewing feeds from unknown sources and the importance of keeping browsers updated should be emphasized. The fix implemented by Opera developers likely involved strengthening input validation for feed URLs, ensuring that all potentially dangerous protocols are properly blocked during preview operations, and implementing more robust sanitization of feed content before display.