CVE-2019-20859 in Mattermost Server
Summary
by MITRE
An issue was discovered in Mattermost Server before 5.15.0. Login access control can be bypassed via crafted input.
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Analysis
by VulDB Data Team • 10/25/2020
The vulnerability identified as CVE-2019-20859 represents a critical authentication bypass flaw within the Mattermost Server platform, affecting versions prior to 5.15.0. This issue stems from inadequate input validation mechanisms that allow malicious actors to circumvent the standard login access controls. The vulnerability specifically targets the server's authentication system, potentially enabling unauthorized users to gain access to protected resources and user accounts without proper credentials. The flaw exists in the server's handling of authentication requests, where crafted input parameters can manipulate the login flow to bypass the intended access control measures.
The technical implementation of this vulnerability involves the manipulation of authentication parameters during the login process, allowing attackers to exploit weaknesses in the server's input sanitization routines. When users attempt to log in, the system processes their credentials through a validation pipeline that fails to properly sanitize or validate certain input fields. This weakness creates an entry point where attackers can submit specially crafted payloads that manipulate the authentication logic. The vulnerability can be classified under CWE-287 which deals with improper handling of authentication tokens and credentials, and aligns with ATT&CK technique T1078 which covers valid accounts and legitimate credentials for unauthorized access. The flaw essentially allows an attacker to bypass the normal authentication checks by leveraging malformed input that the server processes incorrectly.
The operational impact of this vulnerability extends beyond simple unauthorized access, potentially enabling attackers to escalate privileges, access sensitive user data, and compromise the integrity of the entire Mattermost deployment. Organizations using affected versions of Mattermost face significant risks including data breaches, unauthorized communication access, and potential lateral movement within their network infrastructure. The vulnerability affects the core authentication mechanism that protects all user accounts and their associated data within the Mattermost platform, making it a high-priority security concern for any organization relying on this communication system. Attackers could exploit this flaw to gain access to private channels, user messages, file shares, and other confidential information stored within the Mattermost environment.
Mitigation strategies for CVE-2019-20859 primarily focus on immediate version upgrades to Mattermost Server 5.15.0 or later, which includes the necessary patches to address the authentication bypass vulnerability. Organizations should also implement additional security controls such as network segmentation, enhanced monitoring of authentication events, and regular security assessments of their Mattermost deployments. The fix implemented in version 5.15.0 involves strengthening input validation mechanisms and ensuring proper sanitization of authentication parameters to prevent the manipulation of login flows. Security teams should also consider implementing multi-factor authentication as an additional layer of protection, though this does not directly address the specific vulnerability. Organizations should conduct thorough testing of the updated system to ensure that the patch does not introduce any regressions in functionality while also monitoring for any signs of exploitation attempts that may have occurred prior to the patch deployment.