CVE-2021-3055 in PAN-OS
Summary
by MITRE • 09/09/2021
An improper restriction of XML external entity (XXE) reference vulnerability in the Palo Alto Networks PAN-OS web interface enables an authenticated administrator to read any arbitrary file from the file system and send a specifically crafted request to the firewall that causes the service to crash. Repeated attempts to send this request result in denial of service to all PAN-OS services by restarting the device and putting it into maintenance mode. This issue impacts: PAN-OS 8.1 versions earlier than PAN-OS 8.1.20; PAN-OS 9.0 versions earlier than PAN-OS 9.0.14; PAN-OS 9.1 versions earlier than PAN-OS 9.1.10; PAN-OS 10.0 versions earlier than PAN-OS 10.0.6. This issue does not affect Prisma Access.
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Analysis
by VulDB Data Team • 09/10/2021
The vulnerability identified as CVE-2021-3055 represents a critical improper restriction of XML external entity reference flaw within the Palo Alto Networks PAN-OS web interface. This weakness stems from insufficient validation of XML input processing, allowing authenticated administrative users to exploit a fundamental security oversight in the firewall's XML parsing mechanism. The vulnerability specifically affects multiple PAN-OS versions including 8.1.x prior to 8.1.20, 9.0.x prior to 9.0.14, 9.1.x prior to 9.1.10, and 10.0.x prior to 10.0.6, creating a substantial attack surface across the PAN-OS platform. The flaw operates through a classic XXE attack pattern where malicious XML content can reference external entities, potentially exposing sensitive system resources to unauthorized access.
The technical exploitation of this vulnerability enables authenticated administrators to perform arbitrary file reads from the underlying file system, providing attackers with access to sensitive configuration files, credentials, and other system data. This capability extends beyond simple information disclosure to include the potential for privilege escalation and system compromise. The vulnerability also permits the execution of specifically crafted requests that can cause the firewall service to crash, leading to system instability and potential denial of service conditions. The crash mechanism operates through malformed XML processing that triggers internal service failures, ultimately forcing the device to restart and enter maintenance mode.
The operational impact of CVE-2021-3055 extends beyond immediate service disruption to encompass broader security implications for organizations relying on Palo Alto Networks firewalls. The combination of arbitrary file reading capabilities and service crash potential creates a multi-faceted threat that can be leveraged for reconnaissance, data exfiltration, and sustained denial of service attacks. Organizations experiencing repeated exploitation attempts face the risk of complete service outages, potentially affecting network security posture and business continuity. The vulnerability's persistence across multiple PAN-OS versions indicates a systemic issue in XML processing validation that requires comprehensive remediation across affected deployments.
Security professionals should recognize this vulnerability as a direct manifestation of CWE-611, which specifically addresses improper restriction of XML external entity reference, and aligns with ATT&CK technique T1213.002 for Data from Information Repositories. The attack vector represents a privilege escalation pathway that can be exploited by authenticated users, making it particularly dangerous in environments where administrative credentials might be compromised. Organizations must implement immediate mitigation strategies including applying the relevant PAN-OS patches, disabling unnecessary XML processing capabilities, and implementing network segmentation to limit the potential impact of successful exploitation attempts.
Mitigation efforts should prioritize the immediate deployment of PAN-OS updates to versions 8.1.20, 9.0.14, 9.1.10, and 10.0.6 or later, which contain the necessary fixes for the XXE vulnerability. Network administrators should also consider implementing additional controls such as XML input validation, monitoring for suspicious XML processing activities, and establishing robust access controls to limit administrative privileges. The vulnerability's impact on service availability necessitates the implementation of redundant security controls and emergency response procedures to minimize potential downtime and maintain network security during remediation efforts. Organizations should conduct comprehensive vulnerability assessments to identify any potential exploitation attempts and ensure that all affected PAN-OS devices receive immediate patching to prevent unauthorized access to system resources and maintain overall network security posture.