CVE-2017-18036 in Bitbucket Server
Summary
by MITRE
The Github repository importer in Atlassian Bitbucket Server before version 5.3.0 allows remote attackers to determine if a service they could not otherwise reach has open ports via a Server Side Request Forgery (SSRF) vulnerability.
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Analysis
by VulDB Data Team • 01/01/2020
The vulnerability identified as CVE-2017-18036 resides within the GitHub repository importer functionality of Atlassian Bitbucket Server, specifically affecting versions prior to 5.3.0. This represents a critical security flaw that enables remote attackers to perform unauthorized port scanning against internal services that would typically be protected by network segmentation. The vulnerability stems from insufficient input validation and sanitization within the repository import mechanism, allowing malicious actors to craft specially formatted requests that trigger the Bitbucket server to make outbound connections to arbitrary destinations specified by the attacker. This creates a dangerous scenario where attackers can leverage the legitimate import functionality to probe internal network infrastructure and identify open ports without having direct network access to those systems.
The technical implementation of this Server Side Request Forgery vulnerability operates through the manipulation of URL parameters within the repository import process. When a user attempts to import a repository from a GitHub URL, the Bitbucket server performs a server-side request to validate or fetch repository metadata. Attackers can exploit this by providing malicious URLs that contain crafted hostnames or IP addresses, causing the server to establish connections to internal services. The vulnerability is particularly dangerous because it bypasses normal network security controls and can reveal information about internal systems that should remain hidden from external networks. This type of vulnerability is categorized under CWE-918 as Server-Side Request Forgery, which specifically addresses situations where applications make unintended requests to internal resources through server-side processing. The attack vector follows the pattern described in the MITRE ATT&CK framework under T1190 - Proxying, where attackers use legitimate server functionality to indirectly access internal systems.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with valuable reconnaissance data that can inform subsequent attacks. By identifying open ports on internal services, attackers can map the network topology and potentially discover additional vulnerabilities within the internal infrastructure. The vulnerability is particularly concerning in enterprise environments where Bitbucket servers often have access to multiple internal networks and services. Organizations may unknowingly expose sensitive systems to external scanning, potentially revealing database servers, application servers, or other critical infrastructure components that should remain isolated from external access. The implications are significant for organizations following security frameworks such as NIST SP 800-53, which emphasizes the importance of protecting internal network resources from unauthorized access and reconnaissance activities.
Mitigation strategies for CVE-2017-18036 primarily involve upgrading to Atlassian Bitbucket Server version 5.3.0 or later, which includes proper input validation and URL sanitization mechanisms that prevent the exploitation of this vulnerability. Organizations should also implement network segmentation controls to limit the connectivity of their Bitbucket servers to internal services, ensuring that even if the vulnerability is exploited, the attack surface remains minimized. Additional protective measures include implementing web application firewalls that can detect and block suspicious URL patterns, configuring proper network access controls to restrict outbound connections from the Bitbucket server, and conducting regular security assessments to identify similar vulnerabilities in other components. The remediation process should also include monitoring for anomalous outbound network connections that might indicate exploitation attempts, as well as implementing proper logging and alerting mechanisms to detect potential reconnaissance activities targeting internal systems through the vulnerable import functionality.