CVE-2007-5899 in PHP
Summary
by MITRE
The output_add_rewrite_var function in PHP before 5.2.5 rewrites local forms in which the ACTION attribute references a non-local URL, which allows remote attackers to obtain potentially sensitive information by reading the requests for this URL, as demonstrated by a rewritten form containing a local session ID.
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Analysis
by VulDB Data Team • 07/31/2019
The vulnerability described in CVE-2007-5899 represents a significant security flaw in PHP's output buffering mechanism that existed prior to version 5.2.5. This issue specifically affects the output_add_rewrite_var function which is designed to automatically rewrite URLs in HTML output to include session identifiers or other variables. The flaw occurs when PHP processes forms that contain an ACTION attribute pointing to a non-local URL, creating a scenario where sensitive session information could be inadvertently exposed through the rewritten form elements. This vulnerability operates at the application layer and specifically targets the HTTP session management practices within PHP applications.
The technical root cause of this vulnerability stems from improper handling of URL rewriting logic within PHP's output buffering system. When the output_add_rewrite_var function encounters a form with a non-local ACTION attribute, it fails to properly distinguish between local and remote URLs during the rewriting process. This results in session identifiers being injected into the ACTION attribute of forms that reference external domains, potentially exposing sensitive session data to remote servers. The vulnerability is categorized under CWE-200, which deals with Information Exposure Through Output Rewriting, and aligns with ATT&CK technique T1566.001 for Initial Access through Spearphishing Attachment. The flaw demonstrates a classic case of inadequate input validation and URL parsing within the web application framework.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates potential attack vectors for remote adversaries seeking to harvest session identifiers and other sensitive data. Attackers can exploit this weakness by crafting malicious forms that, when processed by vulnerable PHP applications, will rewrite the ACTION attribute to include session IDs or other identifying information. This information can then be captured by the remote server specified in the ACTION attribute, effectively allowing attackers to hijack user sessions or gain insights into the application's internal workings. The vulnerability particularly affects web applications that rely heavily on PHP's output rewriting capabilities for session management and URL normalization, making it a significant concern for enterprise applications and web services.
Mitigation strategies for this vulnerability require immediate patching of affected PHP installations to version 5.2.5 or later where the issue has been resolved. System administrators should also implement proper input validation and URL parsing mechanisms within their applications to prevent the automatic rewriting of forms that reference external domains. Additional protective measures include monitoring network traffic for suspicious patterns in form submissions, implementing web application firewalls to detect and block malicious URL rewriting attempts, and conducting regular security assessments of PHP applications to identify similar vulnerabilities. Organizations should also consider implementing strict access controls and session management policies that minimize the exposure of sensitive session data in URLs and form attributes. The fix implemented in PHP 5.2.5 specifically addresses the URL validation logic within the output_add_rewrite_var function, ensuring that only local URLs are subject to automatic rewriting processes.