CVE-2021-34787 in ASA
Summary
by MITRE • 10/27/2021
A vulnerability in the identity-based firewall (IDFW) rule processing feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to bypass security protections. This vulnerability is due to improper handling of network requests by affected devices configured to use object group search. An attacker could exploit this vulnerability by sending a specially crafted network request to an affected device. A successful exploit could allow the attacker to bypass access control list (ACL) rules on the device, bypass security protections, and send network traffic to unauthorized hosts.
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Analysis
by VulDB Data Team • 07/28/2023
The vulnerability identified as CVE-2021-34787 represents a critical flaw in Cisco's identity-based firewall rule processing mechanism affecting both Adaptive Security Appliance software and Firepower Threat Defense software. This security weakness stems from inadequate validation of network requests when devices are configured with object group search functionality, creating a significant bypass opportunity for unauthenticated remote attackers. The vulnerability specifically targets the processing logic within the identity-based firewall component, which is designed to enforce access control policies based on user identity rather than traditional network addressing.
The technical exploitation of this vulnerability occurs through the improper handling of specially crafted network requests that leverage the object group search feature. When an affected device processes these malformed requests, the identity-based firewall rule processing fails to properly validate the incoming traffic, allowing malicious packets to bypass the standard access control list enforcement mechanisms. This flaw operates at the core of the device's security policy enforcement engine, where the expected behavior of validating network traffic against configured rules is circumvented. The vulnerability manifests when the device's rule processing logic does not adequately account for certain request patterns that can manipulate the object group search functionality to skip security checks entirely.
From an operational standpoint, successful exploitation of CVE-2021-34787 provides attackers with the ability to bypass critical security protections that would normally prevent unauthorized network access. This includes the ability to circumvent access control list rules that are fundamental to network security architecture, allowing malicious traffic to reach unauthorized hosts that would typically be blocked by the firewall. The impact extends beyond simple access bypass to potentially enable lateral movement within networks, data exfiltration, and other malicious activities that rely on evading network-based security controls. This vulnerability essentially undermines the core security model of identity-based firewalls by allowing attackers to manipulate the rule processing logic to achieve unauthorized access.
The vulnerability aligns with CWE-284, which addresses improper access control in software systems, and maps to several ATT&CK techniques including T1071.004 for application layer protocol and T1566 for phishing with a malicious attachment, as attackers could leverage this bypass to establish unauthorized network connections. Organizations using affected Cisco ASA and FTD devices face significant risk exposure, particularly in environments where identity-based security policies are critical for network protection. The remote nature of the exploit means that attackers do not require physical access or credentials to potentially compromise network security, making this vulnerability particularly concerning for enterprise environments.
Mitigation strategies for CVE-2021-34787 should prioritize immediate patch deployment from Cisco, as the vendor has released software updates addressing this specific vulnerability. Network administrators should also implement temporary network segmentation measures to limit potential attack surface, disable object group search functionality where possible, and monitor network traffic for unusual patterns that might indicate exploitation attempts. Additional defensive measures include implementing network-based intrusion detection systems to detect anomalous traffic patterns and establishing strict monitoring of firewall rule processing logs to identify potential bypass attempts. Organizations should also conduct comprehensive vulnerability assessments to identify all affected devices and ensure that patches are applied across the entire network infrastructure.