CVE-2021-3048 in PAN-OS
Summary
by MITRE • 08/12/2021
Certain invalid URL entries contained in an External Dynamic List (EDL) cause the Device Server daemon (devsrvr) to stop responding. This condition causes subsequent commits on the firewall to fail and prevents administrators from performing commits and configuration changes even though the firewall remains otherwise functional. If the firewall then restarts, it results in a denial-of-service (DoS) condition and the firewall stops processing traffic. This issue impacts: PAN-OS 9.0 versions earlier than PAN-OS 9.0.14; PAN-OS 9.1 versions earlier than PAN-OS 9.1.9; PAN-OS 10.0 versions earlier than PAN-OS 10.0.5. PAN-OS 8.1 and PAN-OS 10.1 versions are not impacted.
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Analysis
by VulDB Data Team • 08/16/2021
This vulnerability resides in the Palo Alto Networks PAN-OS firewall software where the Device Server daemon process becomes unresponsive when processing malformed URL entries within External Dynamic Lists. The issue stems from insufficient input validation and error handling mechanisms within the devsrvr component that fails to properly process invalid URL formats. When an attacker or administrator inadvertently introduces malformed URLs into EDL configurations, the daemon enters a non-recoverable state where it ceases to respond to subsequent commit operations. This creates a cascading failure condition where the firewall's configuration management system becomes inaccessible, preventing any further configuration changes despite the underlying hardware and network processing capabilities remaining fully operational.
The technical flaw manifests as a resource management and state handling issue that can be categorized under CWE-248, unspecified error condition, and more specifically aligns with CWE-399 which covers resource management errors. The vulnerability represents a classic denial-of-service condition that operates at the application layer of the firewall's architecture, affecting the configuration management interface rather than the core packet processing functions. The specific daemon process devsrvr demonstrates poor exception handling when encountering malformed input data, leading to a complete service disruption that requires manual intervention or system restart to resolve. This behavior can be mapped to ATT&CK technique T1499.004 which covers network denial of service attacks, though in this case the vulnerability represents an internal failure rather than an external attack vector.
The operational impact of this vulnerability extends beyond simple service interruption as it creates a configuration lockout scenario where administrators cannot apply security updates, modify policies, or perform routine maintenance operations. The firewall continues to process network traffic normally, but the administrative interface becomes completely unusable, creating a false sense of security while simultaneously preventing critical security management functions. When the firewall undergoes a restart to recover from this condition, the entire system experiences a complete denial-of-service state where network traffic processing ceases entirely until manual intervention restores the system. This creates significant operational risk for organizations relying on continuous network security protection, as the firewall becomes effectively non-functional for security management purposes while still potentially processing traffic in a degraded state.
Organizations should immediately implement mitigation strategies including updating to the affected PAN-OS versions that contain the patch for this vulnerability. The recommended approach involves upgrading to PAN-OS 9.0.14, 9.1.9, or 10.0.5 depending on the current version in use. Additionally, administrators should implement strict validation procedures for all external dynamic list entries and establish monitoring mechanisms to detect malformed URL entries before they can cause system disruption. Network segmentation and redundancy measures should be considered to minimize the impact of such failures on critical network infrastructure. Security teams should also implement automated alerting for configuration commit failures and establish incident response procedures specifically addressing this vulnerability to ensure rapid recovery when incidents occur. The patch addresses the root cause by implementing proper input validation and error handling within the devsrvr daemon, preventing malformed URL entries from causing the daemon to enter an unresponsive state and maintaining system availability for both operational and security management functions.