Source: secalert@redhat.com
The mod_security2 module before 2.7.0 for the Apache HTTP Server allows remote attackers to bypass rules, and deliver arbitrary POST data to a PHP application, via a multipart request in which an invalid part precedes the crafted data.
ModSecurity 2.7.0 and earlier for Apache HTTP Server is vulnerable to a critical flaw allowing attackers to bypass security rules and inject malicious POST data into PHP applications. This vulnerability enables remote attackers to execute arbitrary code, potentially leading to complete system compromise and data breaches.
Step 1: Crafting the Malformed Request: The attacker constructs a multipart/form-data POST request. This request includes an invalid or malformed part at the beginning, designed to confuse ModSecurity's parsing engine. This invalid part could be a part with incorrect headers or an incomplete structure.
Step 2: Bypassing Rule Checks: The invalid part causes ModSecurity to misinterpret the request structure. This misinterpretation leads to the subsequent, crafted part containing the malicious payload to bypass the security rules. The rules are not applied to the malicious data.
Step 3: Injecting Malicious Payload: The attacker includes the malicious payload within the second part of the multipart request. This payload is designed to exploit vulnerabilities in the target PHP application, such as SQL injection, cross-site scripting (XSS), or remote code execution (RCE).
Step 4: Delivering the Payload: The crafted request, with the bypassed rules and injected payload, is sent to the vulnerable Apache HTTP Server. The PHP application receives the malicious data.
Step 5: Exploitation: The PHP application processes the malicious data, leading to the attacker's desired outcome, such as unauthorized access, data theft, or system compromise.
The vulnerability stems from a parsing flaw in ModSecurity's handling of multipart/form-data requests. Specifically, the module fails to properly validate the structure of multipart requests, allowing an attacker to craft a request with an invalid part preceding the malicious data. This invalid part confuses the parsing logic, causing the subsequent data (containing the malicious payload) to bypass the security rules designed to filter or block it. The root cause is a lack of robust input validation and improper handling of malformed multipart requests, leading to a logic error in the rule processing engine. The vulnerability allows for rule bypass and arbitrary data injection.
While no specific APTs are definitively linked to this CVE, the ease of exploitation and potential for high impact make it attractive to a wide range of threat actors, including those involved in ransomware campaigns and data theft. This vulnerability is a common target for opportunistic attackers. Not listed on CISA KEV.
Analyze Apache access logs for unusual multipart/form-data POST requests, especially those with malformed headers or unexpected content types.
Monitor ModSecurity audit logs for rule bypasses or unusual activity related to POST requests.
Implement network intrusion detection systems (IDS) with signatures that detect malformed multipart requests or specific attack patterns associated with this vulnerability.
Examine web server logs for suspicious PHP application behavior, such as unexpected file access, database queries, or command execution.
Use file integrity monitoring (FIM) to detect unauthorized changes to PHP application files.
Upgrade ModSecurity to version 2.7.0 or later.
Review and update ModSecurity rules to include specific checks for malformed multipart requests and potential attack vectors.
Implement a Web Application Firewall (WAF) with robust multipart request parsing and validation capabilities.
Regularly update the Apache HTTP Server and PHP application to patch any related vulnerabilities.
Harden the PHP application by implementing secure coding practices, input validation, and output encoding.
Implement a defense-in-depth strategy including network segmentation and intrusion detection/prevention systems.