CVE-2015-7519 in Passenger
Summary
by MITRE
agent/Core/Controller/SendRequest.cpp in Phusion Passenger before 4.0.60 and 5.0.x before 5.0.22, when used in Apache integration mode or in standalone mode without a filtering proxy, allows remote attackers to spoof headers passed to applications by using an _ (underscore) character instead of a - (dash) character in an HTTP header, as demonstrated by an X_User header.
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Analysis
by VulDB Data Team • 07/02/2022
The vulnerability identified as CVE-2015-7519 represents a critical header spoofing flaw within the Phusion Passenger application server software that affects versions prior to 4.0.60 and 5.0.22. This security weakness specifically manifests in the Apache integration mode or standalone mode configurations where no filtering proxy is present to validate header integrity. The flaw exploits the inconsistent handling of HTTP header names by allowing malicious actors to manipulate request headers through the substitution of underscore characters for the standard dash character used in HTTP header naming conventions.
The technical implementation of this vulnerability stems from the software's failure to properly normalize HTTP header names during request processing. When an attacker submits a request containing headers with underscores instead of dashes, the system processes these headers differently than standard HTTP headers, potentially allowing the bypass of security controls that rely on specific header validation. The demonstration case shows how an attacker could submit an X_User header instead of the expected X-User header, enabling the spoofing of user identity information that applications might trust and process accordingly. This behavior creates a path for unauthorized access and potential privilege escalation attacks.
The operational impact of this vulnerability extends beyond simple header manipulation, as it fundamentally undermines the security model of applications relying on Phusion Passenger for request handling. Applications that depend on specific header validation for authentication, authorization, or session management could be compromised through this technique, allowing attackers to impersonate users, bypass access controls, or manipulate application behavior. The vulnerability is particularly dangerous in environments where header-based security mechanisms are critical for maintaining application integrity and user authentication boundaries.
Mitigation strategies for CVE-2015-7519 require immediate deployment of patched versions of Phusion Passenger software, specifically upgrading to version 4.0.60 or 5.0.22 and later. Organizations should also implement additional security controls such as deploying reverse proxies or load balancers that normalize HTTP headers before they reach the application server, ensuring all header names conform to standard HTTP conventions. The vulnerability aligns with CWE-284 access control flaws and can be categorized under ATT&CK technique T1566 for credential access through header manipulation. Network administrators should also consider implementing header validation rules within their web application firewalls to detect and block requests containing non-standard header naming patterns, particularly those using underscores in header names that should normally use dashes.
This vulnerability demonstrates the importance of proper input validation and header normalization in web application servers, as it highlights how seemingly minor implementation details in HTTP header processing can create significant security weaknesses. The flaw serves as a reminder that application server software must maintain strict adherence to HTTP specifications and implement robust sanitization mechanisms for all received data, particularly when that data forms the basis for critical security decisions within applications.