CVE-2025-20339 in SD-WAN vEdge Cloud
Summary
by MITRE • 09/24/2025
A vulnerability in the access control list (ACL) processing of IPv4 packets of Cisco SD-WAN vEdge Software could allow an unauthenticated, remote attacker to bypass a configured ACL.
This vulnerability is due to the improper enforcement of the implicit deny all at the end of a configured ACL. An attacker could exploit this vulnerability by attempting to send unauthorized traffic to an interface on an affected device. A successful exploit could allow the attacker to bypass an ACL on the affected device.
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Analysis
by VulDB Data Team • 09/24/2025
The vulnerability identified as CVE-2025-20339 represents a critical access control flaw within Cisco SD-WAN vEdge Software that fundamentally undermines network security policies. This issue affects the processing of IPv4 packets through the access control list mechanism, creating a scenario where network administrators believe their traffic filtering rules are properly enforced. The vulnerability specifically targets the implicit deny all rule that should automatically terminate all access control lists, which serves as a crucial security boundary in network infrastructure. When this rule fails to function correctly, it creates an unexpected pathway for unauthorized network access that bypasses the intended security controls.
The technical root cause of this vulnerability lies in the improper enforcement of the implicit deny all rule that should be automatically appended to the end of every configured access control list. According to established cybersecurity principles and the Common Weakness Enumeration standard CWE-284, this represents an access control weakness where the system fails to properly enforce the principle of least privilege. The flaw occurs during the packet processing phase when the software does not correctly evaluate whether traffic should be denied by default after all configured rules have been processed. This failure creates a security gap where traffic that should be explicitly denied according to the configured ACL rules can still traverse the network device, effectively neutralizing the access control policy.
The operational impact of this vulnerability is severe and far-reaching for organizations relying on Cisco SD-WAN vEdge Software for their network security. Remote attackers who can reach the affected devices can exploit this flaw to bypass configured access control lists without requiring authentication credentials, making the attack surface extremely broad. This vulnerability directly impacts the CIA triad, specifically compromising the confidentiality and integrity of network communications by allowing unauthorized access to network resources. The attack vector is particularly dangerous because it requires no prior authentication and can be executed from any network location that can reach the vulnerable device, making it a prime target for network reconnaissance and lateral movement activities. Organizations may experience unauthorized data exfiltration, malicious traffic injection, or complete network compromise when this vulnerability is exploited.
Security professionals should implement immediate mitigation strategies to address this vulnerability while more comprehensive solutions are developed. The primary recommendation involves configuring additional security controls outside the affected device to monitor and filter traffic that may be bypassing the ACL enforcement. Network administrators should also consider implementing redundant access control mechanisms such as firewall rules at multiple network layers, network segmentation strategies, and enhanced monitoring of traffic patterns that may indicate exploitation attempts. According to ATT&CK framework category T1071.004 for application layer protocol, this vulnerability creates an opportunity for attackers to leverage network protocols for unauthorized access, making it essential to implement protocol-specific controls and monitoring. Organizations should also conduct thorough network audits to identify all affected devices and prioritize patching efforts based on risk assessment. The vulnerability demonstrates the critical importance of proper access control implementation and the potential consequences when security boundaries are not properly enforced in network infrastructure software.