CVE-2019-20885 in Mattermost Server
Summary
by MITRE
An issue was discovered in Mattermost Server before 5.8.0. It does not always generate a robots.txt file.
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Analysis
by VulDB Data Team • 10/25/2020
The vulnerability identified as CVE-2019-20885 affects Mattermost Server versions prior to 5.8.0 and represents a significant information disclosure risk stemming from the absence of proper web server configuration. This issue falls under the category of insecure default configuration where the application fails to implement standard security measures that should be automatically enforced. The lack of a robots.txt file creates an unintended exposure of sensitive server resources and directories that could be indexed by search engines or accessed by malicious actors. This vulnerability is particularly concerning because it represents a fundamental security misconfiguration that could be exploited to gain unauthorized access to server components or sensitive data.
The technical flaw manifests in the server's failure to generate a robots.txt file during the application startup process or when serving web content. A robots.txt file serves as a standard protocol that instructs web crawlers and search engine bots about which parts of a website should not be accessed or indexed. Without this file, web crawlers may inadvertently discover and index sensitive directories, configuration files, or administrative interfaces that should remain hidden from public access. This misconfiguration creates an attack surface that could be leveraged by threat actors to enumerate server resources, identify potential entry points, or discover sensitive information that might otherwise remain protected. The vulnerability is classified as a configuration management issue that can be addressed through proper server hardening practices and adherence to security baseline configurations.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates opportunities for more sophisticated attacks that could compromise the integrity and confidentiality of the Mattermost server environment. Attackers could potentially use the discovered paths to identify misconfigured services, find backup files, access log files, or locate administrative interfaces that provide elevated privileges. The absence of a robots.txt file also violates fundamental security principles and could result in compliance violations for organizations that must adhere to regulatory requirements such as the general data protection regulation or other information security standards. This vulnerability directly impacts the principle of least privilege by potentially exposing server resources that should remain restricted to authorized personnel only.
Organizations should implement immediate mitigations including upgrading to Mattermost Server version 5.8.0 or later where this vulnerability has been addressed. The recommended approach involves deploying a custom robots.txt file that explicitly disallows access to sensitive directories and server components while maintaining proper access controls and monitoring. Security teams should conduct comprehensive audits of their web server configurations to ensure that all applications properly implement standard security measures including proper robots.txt generation, access control lists, and directory browsing restrictions. Additionally, organizations should consider implementing web application firewalls and monitoring solutions that can detect and prevent unauthorized access attempts to exposed server resources. The vulnerability aligns with CWE-200 (Information Exposure) and could potentially be leveraged as part of broader attack chains that follow the tactics described in the MITRE ATT&CK framework under initial access and reconnaissance phases. Regular security assessments and automated vulnerability scanning should be implemented to identify similar misconfigurations across the entire infrastructure.