CVE-2017-18096 in Application Links
Summary
by MITRE
The OAuth status rest resource in Atlassian Application Links before version 5.2.7, from 5.3.0 before 5.3.4 and from 5.4.0 before 5.4.3 allows remote attackers with administrative rights to access the content of internal network resources via a Server Side Request Forgery (SSRF) by creating an OAuth application link to a location they control and then redirecting access from the linked location's OAuth status rest resource to an internal location. When running in an environment like Amazon EC2, this flaw maybe used to access to a metadata resource that provides access credentials and other potentially confidential information.
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Analysis
by VulDB Data Team • 01/22/2020
The vulnerability identified as CVE-2017-18096 represents a critical Server Side Request Forgery (SSRF) flaw within Atlassian Application Links, specifically affecting versions prior to 5.2.7, 5.3.4, and 5.4.3. This security weakness stems from the improper validation of OAuth application link configurations, allowing authenticated attackers with administrative privileges to manipulate the OAuth status REST resource. The flaw operates by enabling malicious actors to establish OAuth application links pointing to controlled external endpoints, which then serve as intermediaries for redirecting requests to internal network resources that would otherwise be inaccessible from the public internet.
The technical implementation of this vulnerability exploits the trust relationship established between Atlassian applications and external OAuth endpoints. When an administrator creates an OAuth application link, the system performs validation checks that fail to adequately verify the destination of the OAuth status REST resource. This oversight permits attackers to craft malicious OAuth configurations that redirect traffic from the external controlled endpoint back to internal resources within the organization's network. The vulnerability specifically affects the OAuth status REST resource, which is designed to communicate with external services but lacks proper input sanitization and destination validation mechanisms. This flaw aligns with CWE-918, which categorizes Server-Side Request Forgery vulnerabilities as those where an application is induced to make HTTP requests to an unintended destination.
The operational impact of CVE-2017-18096 extends beyond simple unauthorized access to internal resources, particularly in cloud environments such as Amazon EC2. Attackers can leverage this vulnerability to access metadata services that provide sensitive information including access credentials, instance identifiers, and other potentially confidential data. This capability transforms a simple SSRF vulnerability into a significant reconnaissance and privilege escalation tool, as the metadata service in EC2 environments contains credentials that can be used to access additional cloud resources. The vulnerability's exploitation requires only administrative access to the Atlassian application, making it particularly dangerous as it can be leveraged by insiders or compromised administrative accounts to gain unauthorized access to internal systems and data.
Organizations should implement multiple layers of mitigation strategies to address this vulnerability effectively. Immediate remediation involves upgrading Atlassian Application Links to versions 5.2.7, 5.3.4, or 5.4.3, which contain the necessary patches to prevent the manipulation of OAuth status REST resources. Network-level protections should include implementing strict firewall rules that restrict outbound connections from Atlassian servers to internal resources, particularly those that are sensitive or contain credentials. Additionally, organizations should consider implementing network segmentation and using tools like AWS Security Groups to limit access to internal metadata services, ensuring that only authorized systems can reach these sensitive endpoints. The ATT&CK framework categorizes this type of vulnerability under T1071.004 for Application Layer Protocol: DNS and T1046 for Network Service Scanning, highlighting the reconnaissance and access patterns that attackers employ when exploiting such SSRF vulnerabilities. Organizations should also implement monitoring and logging of OAuth application link creation activities to detect potential malicious configuration changes and establish incident response procedures specifically tailored to address SSRF exploitation attempts.