CVE-2023-45132 in NAXSI
Summary
by MITRE • 10/25/2023
NAXSI is an open-source maintenance web application firewall (WAF) for NGINX. An issue present starting in version 1.3 and prior to version 1.6 allows someone to bypass the WAF when a malicious `X-Forwarded-For` IP matches `IgnoreIP` `IgnoreCIDR` rules. This old code was arranged to allow older NGINX versions to also support `IgnoreIP` `IgnoreCIDR` when multiple reverse proxies were present. The issue is patched in version 1.6. As a workaround, do not set any `IgnoreIP` `IgnoreCIDR` for older versions.
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Analysis
by VulDB Data Team • 10/31/2023
The vulnerability CVE-2023-45132 affects NAXSI, an open-source web application firewall designed for NGINX environments. This security flaw exists in versions 1.3 through 1.5, creating a significant bypass opportunity for attackers who can manipulate the X-Forwarded-For HTTP header to circumvent WAF protections. The issue stems from the implementation of legacy support mechanisms that were originally intended to accommodate older NGINX versions where multiple reverse proxies could complicate IP address tracking. The NAXSI WAF uses IgnoreIP and IgnoreCIDR rules to define trusted IP addresses or networks that should be exempt from certain security checks, but this functionality has been exploited to allow malicious traffic to bypass protection mechanisms.
The technical flaw manifests when a malicious actor crafts a specially formatted X-Forwarded-For header that matches existing IgnoreIP or IgnoreCIDR rules within the WAF configuration. This creates a dangerous condition where the WAF incorrectly identifies malicious traffic as trusted, effectively disabling security controls for that specific request. The vulnerability represents a classic case of improper input validation and access control enforcement, aligning with CWE-284 Access Control Issues and CWE-347 Improper Verification of Cryptographic Signature. The flaw specifically exploits the trust model established by the IgnoreIP and IgnoreCIDR directives, which were designed to handle legitimate scenarios involving multiple proxy layers but have been misconfigured or exploited to undermine security.
The operational impact of this vulnerability is substantial for organizations relying on NAXSI WAF protection, as it allows attackers to bypass security controls that would normally detect and block malicious requests. This could enable various attack vectors including SQL injection, cross-site scripting, and other web application vulnerabilities that the WAF was designed to prevent. The vulnerability affects the core security posture of NGINX environments, potentially allowing persistent threats to establish footholds within networks by evading detection mechanisms. Organizations using older NAXSI versions face particular risk since the fix requires upgrading to version 1.6 or later, which may involve compatibility considerations with existing infrastructure.
The recommended mitigation strategy involves upgrading to NAXSI version 1.6 or later where the vulnerability has been patched. For organizations unable to upgrade immediately, the workaround of not setting any IgnoreIP or IgnoreCIDR rules provides temporary protection, though this may impact legitimate multi-proxy configurations. Security teams should conduct thorough audits of their NAXSI configurations to identify any existing IgnoreIP or IgnoreCIDR rules that could be exploited. The vulnerability also highlights the importance of maintaining up-to-date security software and the risks associated with legacy code implementations that persist beyond their intended support periods. This case demonstrates how seemingly benign configuration options can create security vulnerabilities when not properly validated against potential attack vectors, aligning with ATT&CK technique T1071.004 Application Layer Protocol: DNS and T1566.001 Phishing: Spearphishing Attachment. Organizations should implement regular security assessments to identify and remediate similar configuration vulnerabilities in their web application firewall implementations.