CVE-2002-1276 in SquirrelMail
Summary
by MITRE
An incomplete fix for a cross-site scripting (XSS) vulnerability in SquirrelMail 1.2.8 calls the strip_tags function on the PHP_SELF value but does not save the result back to that variable, leaving it open to cross-site scripting attacks.
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Analysis
by VulDB Data Team • 05/10/2019
The vulnerability described in CVE-2002-1276 represents a critical security flaw in SquirrelMail version 1.2.8 that demonstrates the dangers of incomplete security patches. This issue specifically targets the cross-site scripting protection mechanisms within the email client's web interface, where a flawed remediation attempt has inadvertently created a persistent security risk. The vulnerability arises from the improper handling of user input through the PHP_SELF server variable, which is commonly used in web applications to reference the current script's URL. When SquirrelMail attempted to address a previous XSS vulnerability by implementing the strip_tags function, the developers failed to properly assign the sanitized output back to the original variable, creating a security gap that attackers could exploit.
The technical implementation of this vulnerability stems from the fundamental flaw in the patch logic itself. The strip_tags function in PHP is designed to remove HTML and PHP tags from a string, which is a standard approach for preventing XSS attacks by eliminating potentially malicious markup. However, in this case, the developers called strip_tags on the PHP_SELF value but failed to reassign the returned sanitized string back to the PHP_SELF variable. This creates a situation where the original unfiltered value remains accessible to the application's processing logic, allowing malicious users to inject script code through the URL parameter that gets passed to the vulnerable application. The PHP_SELF variable contains the filename of the current script, and when this value is used in the application's output without proper sanitization, it becomes a prime target for cross-site scripting attacks that can execute arbitrary JavaScript in the context of a victim's browser.
The operational impact of this vulnerability extends beyond simple data theft or session hijacking, as it represents a complete bypass of the intended security controls. Attackers can craft malicious URLs that contain script payloads which will execute when the vulnerable SquirrelMail application processes the PHP_SELF variable in its output generation. This allows for a wide range of malicious activities including cookie theft, session fixation, redirection to malicious sites, and potential privilege escalation within the web application. The vulnerability is particularly concerning because it affects the core authentication and navigation functionality of SquirrelMail, potentially allowing unauthorized access to user mailboxes and sensitive email communications. From an attacker's perspective, this vulnerability provides a straightforward path to compromise user sessions and gain access to confidential email data, making it a high-value target in web application security assessments.
This vulnerability aligns with several established security frameworks and threat models, particularly CWE-79 which defines cross-site scripting as a fundamental web application security weakness. The incomplete patch approach also reflects common patterns seen in the ATT&CK framework under the technique of privilege escalation through software vulnerabilities, where developers inadvertently create new attack vectors through misguided security fixes. Organizations running SquirrelMail 1.2.8 would be particularly vulnerable to this type of attack, as the flaw affects the application's core input sanitization mechanisms. The remediation process requires not only updating to a patched version of SquirrelMail but also implementing proper input validation and output encoding practices. Security teams should implement comprehensive monitoring for suspicious URL patterns and consider implementing web application firewalls to detect and block known XSS attack patterns. Additionally, this vulnerability underscores the importance of thorough testing and validation of security patches, as demonstrated by the fact that a well-intentioned fix actually created a more severe vulnerability than the original issue, highlighting the critical need for security professionals to understand the full implications of their code changes and to conduct proper regression testing before deploying security updates.