CVE-2001-0108 in PHP
Summary
by MITRE
PHP Apache module 4.0.4 and earlier allows remote attackers to bypass .htaccess access restrictions via a malformed HTTP request on an unrestricted page that causes PHP to use those access controls on the next page that is requested.
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Analysis
by VulDB Data Team • 07/19/2019
The vulnerability identified as CVE-2001-0108 represents a critical access control flaw within the PHP Apache module version 4.0.4 and earlier. This issue stems from a fundamental design weakness in how PHP processes HTTP requests and applies access controls, particularly when dealing with .htaccess files that contain restrictive permissions. The vulnerability operates through a sophisticated manipulation of request handling sequences that allows malicious actors to exploit the module's behavior during specific processing states. The flaw specifically targets the interaction between PHP's internal request parsing mechanism and Apache's access control system, creating an unexpected pathway for unauthorized access.
The technical implementation of this vulnerability occurs when a remote attacker crafts a malformed HTTP request that appears to be directed at an unrestricted page within the web application. This particular request structure causes PHP to improperly handle the access control enforcement mechanism, specifically triggering a state where the module fails to properly distinguish between restricted and unrestricted resources. The vulnerability exploits a race condition or state management flaw where the access control rules defined in .htaccess files are inadvertently applied to subsequent requests, even when those requests should be permitted to proceed without restriction. This behavior violates fundamental security principles of least privilege and proper access control enforcement.
The operational impact of this vulnerability extends far beyond simple unauthorized access, as it can enable attackers to bypass critical security controls that are meant to protect sensitive resources and directories. When an attacker successfully exploits this flaw, they can gain access to resources that should be restricted, potentially leading to data exposure, privilege escalation, or further exploitation of the web application. The vulnerability is particularly dangerous because it operates silently and can be difficult to detect through conventional monitoring systems. The attack vector requires minimal sophistication but can produce significant consequences, making it a preferred target for automated exploitation tools and malicious actors seeking to compromise web applications running vulnerable PHP versions.
Organizations affected by this vulnerability should implement immediate mitigations including upgrading to PHP versions 4.0.5 or later where this issue has been resolved through proper state management and request handling improvements. The fix addresses the core problem by ensuring that access control decisions are properly isolated between different request contexts, preventing the contamination of access control state between unrestricted and restricted pages. Security practitioners should also consider implementing additional layers of protection including web application firewalls that can detect and block malformed HTTP requests, as well as regular security audits of access control configurations. This vulnerability aligns with CWE-284, which addresses improper access control, and represents a specific implementation flaw in the Apache module's request processing that enables privilege escalation through improper resource access enforcement. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically targeting the access control mechanisms that protect sensitive application resources.