CVE-2009-1234 in Web Browser
Summary
by MITRE
Opera 9.64 allows remote attackers to cause a denial of service (application crash) via an XML document containing a long series of start-tags with no corresponding end-tags. NOTE: it was later reported that 9.52 is also affected.
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Analysis
by VulDB Data Team • 04/19/2025
This vulnerability affects opera web browser version 9.64 and potentially 9.52, representing a denial of service flaw that can be exploited remotely through malformed xml documents. The vulnerability stems from the browser's insufficient handling of xml parsing logic when encountering documents containing extended sequences of start-tags without corresponding end-tags. This specific weakness creates a condition where the browser's xml parser becomes overwhelmed and eventually crashes, resulting in complete application failure and denial of service for the affected user. The flaw demonstrates poor input validation and resource management within the browser's xml processing subsystem, which fails to implement adequate safeguards against malformed input patterns that could lead to resource exhaustion or stack overflow conditions during parsing operations.
The technical execution of this attack requires an attacker to craft a specially formatted xml document containing a prolonged series of unclosed start-tags that can cause the browser's xml parser to enter an infinite loop or consume excessive memory resources. This type of vulnerability is categorized as a buffer over-read or parsing error condition that falls under the broader category of improper input validation issues. The operational impact extends beyond simple application instability as it can be leveraged by malicious actors to disrupt service availability for legitimate users, potentially affecting web applications that rely on opera browser functionality or users who may inadvertently encounter such malformed content while browsing. The vulnerability also represents a classic example of how xml parsing libraries can be susceptible to malformed input that leads to resource exhaustion rather than direct code execution.
From a security perspective, this vulnerability highlights the importance of robust input sanitization and validation mechanisms within web browsers, particularly in xml processing components that are often overlooked in security reviews. The flaw aligns with common weakness enumerations such as cwe-129 and cwe-134 which address improper input validation and buffer overflows respectively. The attack vector demonstrates characteristics consistent with the attack technique known as application level denial of service within the attack pattern taxonomy. The vulnerability's exploitation potential is enhanced by the fact that xml documents are commonly encountered during web browsing, making this a particularly concerning flaw for browser vendors and users alike. Organizations should consider this vulnerability in their risk assessments and ensure that browser updates are applied promptly to address such parsing-related security issues.
The remediation approach for this vulnerability involves implementing proper xml parsing validation that includes limits on tag nesting depth, maximum tag count, and resource allocation during parsing operations. Browser vendors should implement input sanitization measures that detect and reject malformed xml content before it can cause resource exhaustion. Additionally, implementing timeout mechanisms and stack depth monitoring during xml processing can prevent exploitation of similar parsing vulnerabilities. Security teams should monitor for similar vulnerabilities in xml processing libraries and ensure that all browser components undergo thorough security testing for input validation weaknesses. The vulnerability also underscores the importance of maintaining up-to-date browser versions and implementing network-based security controls that can detect and block malicious xml content before it reaches end-user browsers.
This particular vulnerability demonstrates the ongoing challenges faced by web browser vendors in securing complex xml processing functionality. The flaw represents a fundamental issue in how browsers handle malformed input and highlights the need for more sophisticated error handling and resource management within parsing components. The fact that multiple versions within the 9.x series were affected indicates that this was likely a systemic issue rather than an isolated incident, suggesting that similar vulnerabilities may exist in other parsing components. The vulnerability's classification as a denial of service rather than a code execution flaw does not diminish its security impact, as availability of web services remains a critical concern for both users and organizations. Proper implementation of xml parsing security measures including input validation, resource limits, and error handling can significantly reduce the risk of similar vulnerabilities in future browser versions.