CVE-2021-1501 in ASA
Summary
by MITRE • 04/30/2021
A vulnerability in the SIP inspection engine of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a crash and reload of an affected device, resulting in a denial of service (DoS) condition.The vulnerability is due to a crash that occurs during a hash lookup for a SIP pinhole connection. An attacker could exploit this vulnerability by sending crafted SIP traffic through an affected device. A successful exploit could allow the attacker to cause a crash and reload of the affected device.
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Analysis
by VulDB Data Team • 07/28/2023
This vulnerability resides within the Session Initiation Protocol inspection engine of Cisco's security appliances, specifically affecting Adaptive Security Appliance software versions 9.1 through 9.12 and Firepower Threat Defense software versions 6.2 through 6.6. The flaw manifests as a critical memory access issue during hash table operations when processing SIP pinhole connections, creating a condition where legitimate network traffic can trigger a system crash. The vulnerability stems from insufficient input validation and error handling within the SIP protocol processing module, which fails to properly validate hash lookup parameters before attempting memory access operations. This represents a classic buffer over-read or hash collision scenario that can be exploited through malformed SIP packets, making it particularly dangerous as it requires no authentication credentials to exploit.
The technical exploitation occurs when an attacker crafts malicious SIP traffic containing specially formatted pinhole connection requests that cause the ASA or FTD device to perform an invalid hash lookup operation. The device's processing engine attempts to access memory locations outside the valid hash table boundaries, leading to an immediate system crash and subsequent automatic reload of the affected appliance. This behavior directly violates the principle of least privilege and system stability, as normal network operations can be disrupted by malicious input. The vulnerability's impact is amplified by the fact that SIP traffic often flows through firewalls and security appliances as part of VoIP communications, making the attack surface broader than typical network protocol vulnerabilities. The underlying flaw can be classified as a CWE-125 out-of-bounds read, which is categorized under the broader category of memory safety issues in the Common Weakness Enumeration taxonomy.
The operational consequences of this vulnerability extend beyond simple service disruption to potentially compromise network security infrastructure. When an affected device crashes and reloads, it creates temporary network gaps that attackers could exploit for further malicious activities, including bypassing security controls during the recovery period. The DoS condition affects the availability of critical network services, as the security appliance becomes unavailable during the restart process, potentially leaving network segments unprotected. This vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under the T1498 tactic for network denial of service, where attackers leverage system weaknesses to disrupt availability. Organizations using Cisco ASA or FTD devices may experience significant operational impact, including potential service interruptions for VoIP communications and general network instability during the device recovery process, particularly in environments where these appliances serve as primary network security gateways.
Mitigation strategies should prioritize immediate patch deployment for affected software versions, as Cisco has released security advisories addressing this specific vulnerability. Network administrators should implement rate limiting and access control lists to restrict SIP traffic flow through affected devices, while also monitoring for anomalous SIP packet patterns that might indicate exploitation attempts. The implementation of redundant security appliances and proper network segmentation can help minimize the impact of such vulnerabilities on overall network availability. Organizations should also consider deploying intrusion detection systems specifically configured to detect and alert on malformed SIP traffic patterns that could indicate exploitation attempts. Additionally, regular security assessments and vulnerability scanning should be conducted to identify other potential weaknesses in the network infrastructure that could be leveraged in combination with this vulnerability. The remediation process requires careful planning to avoid service disruption during patch deployment, particularly in mission-critical environments where network availability is paramount.