CVE-2019-20104 in Atlassian Crowd
Summary
by MITRE
The OpenID client application in Atlassian Crowd before version 3.6.2, and from version 3.7.0 before 3.7.1 allows remote attackers to perform a Denial of Service attack via an XML Entity Expansion vulnerability.
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Analysis
by VulDB Data Team • 03/28/2024
The vulnerability identified as CVE-2019-20104 represents a critical XML External Entity (XXE) flaw within the OpenID client implementation of Atlassian Crowd software. This weakness affects versions prior to 3.6.2 and specifically impacts versions from 3.7.0 through 3.7.0, creating a window of exposure where attackers can exploit the system's handling of XML data. The vulnerability stems from insufficient input validation and sanitization within the XML parsing mechanisms that process OpenID responses, allowing malicious actors to craft specially formatted XML payloads that trigger resource exhaustion conditions.
The technical exploitation of this vulnerability occurs through XML Entity Expansion attacks, where an attacker constructs XML content containing recursive entity definitions that cause the parser to expand entities repeatedly until system resources are depleted. This particular implementation flaw resides in the OpenID client component of Crowd, which processes authentication responses from OpenID providers. When the system receives a crafted XML response containing malicious entity declarations, the XML parser processes these entities without proper restrictions, leading to exponential resource consumption. The vulnerability specifically targets the XML parsing libraries used by the OpenID client, making it particularly dangerous as it can be triggered through legitimate authentication flows that involve OpenID providers.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire authentication infrastructure of affected systems. Attackers can initiate sustained denial of service attacks that consume CPU cycles and memory resources, effectively preventing legitimate users from accessing Crowd services. The attack vector is particularly concerning because it can be executed remotely without requiring authentication credentials, making it an attractive target for malicious actors seeking to disrupt business operations. Organizations relying on Crowd for user management and authentication may experience complete service outages, impacting access to critical applications and systems that depend on Crowd for identity management.
Mitigation strategies for CVE-2019-20104 should prioritize immediate patching of affected versions to 3.6.2 or 3.7.1 and later releases where the XXE vulnerability has been addressed. Security teams should implement XML parser configuration changes to disable external entity resolution andDTD processing within the affected applications. Network-level protections including firewall rules and intrusion detection systems can help monitor for suspicious XML traffic patterns, while application-level monitoring should track resource consumption metrics to detect potential exploitation attempts. Organizations should also consider implementing additional authentication mechanisms and redundancy measures to maintain service availability during potential attack scenarios. This vulnerability aligns with CWE-611 (Improper Restriction of XML External Entity Reference) and maps to ATT&CK technique T1499.004 (Endpoint Denial of Service) within the attack framework, highlighting the need for comprehensive defensive measures across multiple security layers to protect against such resource exhaustion attacks.