CVE-2019-20866 in Mattermost Server
Summary
by MITRE
An issue was discovered in Mattermost Server before 5.12.0. Use of a Proxy HTTP header, rather than the source address in an IP packet header, for obtaining IP address information was mishandled.
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Analysis
by VulDB Data Team • 10/25/2020
The vulnerability identified as CVE-2019-20866 represents a significant security flaw in Mattermost Server versions prior to 5.12.0 where the application improperly handled IP address information derived from HTTP proxy headers. This issue stems from the server's reliance on the Proxy HTTP header for determining client IP addresses rather than utilizing the more reliable source address information contained within IP packet headers. The improper handling of this information creates a potential vector for IP address spoofing and address manipulation attacks that could compromise the integrity of client identification within the messaging platform.
This vulnerability falls under the category of improper input validation and information exposure, aligning with CWE-20 which encompasses various forms of input validation failures and CWE-200 which addresses information exposure. The flaw essentially allows malicious actors to manipulate the perceived source IP address of requests by injecting false values into the Proxy header, potentially bypassing IP-based access controls, rate limiting mechanisms, and security policies that depend on accurate client IP identification. The issue directly impacts the server's ability to correctly authenticate and authorize users based on their actual network locations.
The operational impact of this vulnerability extends beyond simple IP address spoofing to encompass broader security implications for Mattermost deployments. Attackers could exploit this weakness to circumvent IP-based restrictions, potentially gaining unauthorized access to restricted channels or features, conducting denial of service attacks by appearing to originate from trusted IP addresses, or evading logging and monitoring systems that rely on accurate IP address information for security analytics. This vulnerability particularly affects organizations that depend on IP-based security controls within their Mattermost implementations, undermining the trust model that should exist between the application and its users.
Organizations should immediately upgrade to Mattermost Server version 5.12.0 or later to remediate this vulnerability, as this release includes proper handling of IP address information through more secure methods that prioritize source IP packet headers over potentially manipulated HTTP proxy headers. Additional mitigations include implementing proper header validation mechanisms, configuring network firewalls to strip or validate proxy headers before they reach the application server, and establishing monitoring for unusual patterns in IP address information that might indicate exploitation attempts. Security teams should also review existing IP-based access control lists and security policies to ensure they remain effective against potential exploitation of this vulnerability, as the flaw could enable attackers to bypass existing protections that depend on accurate client IP identification.