CVE-2013-5526 in IP Phone
Summary
by MITRE
Cisco 9900 fourth-generation IP phones do not properly perform SDP negotiation, which allows remote attackers to cause a denial of service (device reboot) via crafted SDP packets, aka Bug ID CSCuf06698.
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Analysis
by VulDB Data Team • 03/24/2019
The vulnerability identified as CVE-2013-5526 affects Cisco 9900 fourth-generation IP phones, representing a critical flaw in the session description protocol (SDP) negotiation process. This issue stems from insufficient validation of SDP packets received by the affected telephony devices, creating a pathway for malicious actors to exploit the system through carefully crafted network traffic. The vulnerability specifically targets the device's handling of session description protocol information that is essential for establishing and maintaining voice communication sessions over IP networks. When the phone receives malformed SDP packets, the device fails to properly process these packets and instead experiences a complete system crash leading to an automatic reboot. This behavior constitutes a denial of service condition that can be remotely triggered without requiring any authentication or privileged access to the network infrastructure.
The technical implementation of this vulnerability resides in the phone's SDP parser which lacks proper input validation mechanisms and error handling routines. When the device encounters SDP packets containing unexpected or malformed parameters, the parsing routine fails catastrophically rather than gracefully handling the error condition. This failure mode triggers a system-level exception that causes the phone's operating system to restart automatically, resulting in immediate service disruption for all ongoing and pending voice communications. The vulnerability is particularly concerning because SDP packets are routinely exchanged during normal phone operation as part of the SIP signaling process, making the attack surface accessible through legitimate network traffic without requiring specialized attack tools or privileged network access. The affected Cisco 9900 IP phones operate under the assumption that SDP information originates from trusted sources within the local network, failing to implement adequate defenses against malformed input from external or compromised network entities.
The operational impact of this vulnerability extends beyond simple service interruption to potentially disrupt business communications across enterprise networks where these phones are deployed. Organizations relying on Cisco 9900 IP phones for critical voice communications may experience significant downtime during attack scenarios, particularly in environments where multiple phones are simultaneously compromised. The automatic reboot behavior means that attackers can effectively create persistent denial of service conditions by repeatedly sending malicious SDP packets, causing phones to continuously restart and preventing users from establishing reliable voice connections. Network administrators may also face challenges in identifying and isolating compromised devices since the reboot behavior obscures the attack signature, making forensic analysis more difficult. The vulnerability affects the availability aspect of the CIA triad, specifically targeting the system's ability to maintain continuous operation and service delivery to authorized users.
Mitigation strategies for CVE-2013-5526 should focus on network-level protections and device firmware updates to address the underlying parsing vulnerability. Cisco has released security advisories and firmware updates that implement proper SDP packet validation and error handling mechanisms to prevent the malformed packet processing that leads to system crashes. Network segmentation and access control measures can help limit the exposure of affected phones to potentially malicious SDP traffic by implementing firewalls and access control lists that filter incoming packets. Additionally, implementing network monitoring solutions that can detect unusual patterns of SDP packet exchanges may provide early warning capabilities for potential attacks. Organizations should also consider deploying intrusion detection systems that can identify and alert on suspicious SDP packet structures that match known attack patterns. The implementation of these mitigations aligns with the principle of defense in depth, as outlined in various cybersecurity frameworks including the NIST Cybersecurity Framework and ISO 27001 standards. This vulnerability demonstrates the importance of proper input validation and error handling in embedded systems, a principle that corresponds to CWE-707 and CWE-248, which address improper handling of exceptions and inadequate error handling in software applications. The attack vector for this vulnerability maps to the MITRE ATT&CK framework's T1499.004 technique for network denial of service, emphasizing the need for robust network infrastructure security practices to prevent exploitation of similar vulnerabilities in telephony systems.