CVE-2018-9230 in OpenResty
Summary
by MITRE
In OpenResty before 1.13.6.1, URI parameters were obtained using the ngx.req.get_uri_args and ngx.req.get_post_args functions that ignore parameters beyond the hundredth one, which might allow remote attackers to bypass intended access restrictions or interfere with certain Web Application Firewall (ngx_lua_waf or X-WAF) products.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability identified as CVE-2018-9230 affects OpenResty versions prior to 1.13.6.1 and represents a critical input validation flaw that undermines the security of web applications deployed behind this reverse proxy and application server platform. This issue specifically targets the ngx.req.get_uri_args and ngx.req.get_post_args functions within the ngx_lua module, which are commonly used to extract and process HTTP request parameters. The flaw manifests when the web application processes URI parameters beyond the hundredth position, as the affected functions silently discard these additional parameters without any indication to the calling application code. This behavior creates a potential security bypass vector that could be exploited by remote attackers to circumvent access controls and security mechanisms implemented within web applications. The vulnerability stems from a fundamental limitation in how parameter parsing is handled within the OpenResty Lua integration, where the system fails to properly handle parameter arrays exceeding 100 elements, effectively truncating legitimate parameter data.
The technical implementation of this vulnerability lies in the internal parameter parsing logic of the OpenResty framework, where the ngx_lua module processes HTTP request parameters using fixed-size buffers or arrays that can only accommodate up to 100 parameters. This limitation directly violates the principle of least privilege and input validation, as the system does not properly validate or handle parameter overflow conditions. When an attacker crafts a malicious request containing more than 100 parameters, the system processes only the first 100 parameters and discards the remainder, potentially allowing unauthorized access to resources or functionality that should be protected. The vulnerability is particularly concerning because it operates silently without generating any error messages or exceptions, making detection extremely difficult for security monitoring systems. This behavior creates a false sense of security for applications that rely on parameter validation and access control mechanisms, as the system appears to function normally while silently discarding critical security-relevant parameters.
The operational impact of CVE-2018-9230 extends beyond simple parameter truncation and can severely compromise web application security, particularly when combined with existing security controls like Web Application Firewalls. Attackers can exploit this vulnerability by crafting requests with more than 100 parameters where the 101st parameter contains malicious data or access control bypass information, effectively rendering security mechanisms ineffective. This flaw directly impacts the security posture of applications using ngx_lua_waf or X-WAF products, as these security solutions may incorrectly process requests that contain parameter overflow conditions, leading to false negatives in threat detection. The vulnerability creates a scenario where legitimate access control parameters are ignored while malicious parameters are processed, potentially allowing unauthorized access to restricted resources. From an ATT&CK framework perspective, this vulnerability maps to techniques involving command and control communication, privilege escalation, and defense evasion, as attackers can manipulate parameter processing to bypass security controls without generating detectable anomalies.
Organizations using affected versions of OpenResty should prioritize immediate remediation through patch updates to version 1.13.6.1 or later, as this vulnerability can be exploited to bypass critical access controls and security mechanisms. Additionally, administrators should implement parameter validation at multiple layers of their security infrastructure, including WAF rules that monitor for unusual parameter counts and behavioral anomalies in application traffic. The mitigation strategy should include monitoring for requests containing excessive parameters that may indicate exploitation attempts, as well as implementing application-level checks to validate parameter processing and ensure that all expected parameters are properly handled. Security teams should also consider implementing network-level controls that can detect and block suspicious parameter patterns that may indicate exploitation of this vulnerability. This vulnerability serves as a reminder of the importance of thorough input validation and the potential security implications of seemingly minor implementation limitations in core web infrastructure components, particularly when these components interact with security-critical functions like access control and threat detection. The issue aligns with CWE-129, which addresses insufficient input validation, and demonstrates how parameter handling limitations can create security bypass opportunities that compromise the integrity of security controls.