CVE-2015-2841 in Netscaler
Summary
by MITRE
Citrix NetScaler AppFirewall, as used in NetScaler 10.5, allows remote attackers to bypass intended firewall restrictions via a crafted Content-Type header, as demonstrated by the application/octet-stream and text/xml Content-Types.
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Analysis
by VulDB Data Team • 07/29/2025
The vulnerability identified as CVE-2015-2841 affects Citrix NetScaler AppFirewall versions prior to 10.5, representing a critical security flaw that undermines the intended protection mechanisms of the application firewall. This vulnerability resides within the content-type validation logic of the NetScaler appliance, specifically targeting how the system processes and evaluates HTTP Content-Type headers. The flaw enables malicious actors to craft specially formatted Content-Type headers that bypass the configured firewall restrictions, effectively allowing unauthorized access to protected resources.
The technical implementation of this vulnerability stems from insufficient validation of Content-Type header values within the AppFirewall's inspection engine. When processing incoming HTTP requests, the NetScaler appliance fails to properly sanitize or validate specific Content-Type values such as application/octet-stream and text/xml, which should typically be subject to strict access controls. Attackers can exploit this by crafting HTTP requests with these specific content types, causing the appliance to either ignore the configured security policies or incorrectly classify the traffic as legitimate. This bypass occurs because the AppFirewall's rule engine does not adequately distinguish between trusted and untrusted content types, creating a pathway for malicious traffic to traverse the security boundary without proper inspection.
The operational impact of CVE-2015-2841 extends beyond simple access bypass, as it fundamentally compromises the integrity of the security controls implemented by organizations using Citrix NetScaler appliances. This vulnerability can enable attackers to bypass web application firewalls, potentially leading to data exfiltration, injection attacks, or unauthorized access to backend systems. The attack vector is particularly concerning because it requires minimal sophistication to execute, making it attractive to threat actors who seek to exploit weaknesses in web application security. Organizations relying on NetScaler appliances for protecting web applications face significant risk of compromise, as this vulnerability can be leveraged to circumvent security policies that should prevent malicious content from reaching target applications.
Mitigation strategies for CVE-2015-2841 primarily involve upgrading to Citrix NetScaler 10.5 or later versions where the vulnerability has been addressed through enhanced Content-Type validation mechanisms. Organizations should also implement additional monitoring and logging procedures to detect anomalous Content-Type header usage patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-20, which describes improper input validation, and represents a specific instance of how insufficient sanitization of user-supplied data can lead to security bypasses. From an ATT&CK framework perspective, this vulnerability maps to techniques involving bypassing security controls and command and control communications, as attackers can leverage the bypass to establish persistent access or exfiltrate data through previously restricted channels.
Organizations should conduct comprehensive vulnerability assessments to identify all instances of affected NetScaler appliances within their infrastructure and prioritize remediation efforts accordingly. The remediation process should include not only software updates but also verification of firewall rule configurations to ensure that content-type based restrictions are properly enforced. Additionally, implementing network segmentation and additional layers of security controls can provide defense-in-depth protection against exploitation attempts. Regular security audits of web application firewalls and continuous monitoring of traffic patterns should be established to detect potential exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation and the potential consequences when security controls fail to properly validate user-supplied data elements, particularly those that can be manipulated to bypass security policies.