CVE-2019-1635 in IP Phone 7800
Summary
by MITRE
A vulnerability in the call-handling functionality of Session Initiation Protocol (SIP) Software for Cisco IP Phone 7800 Series and 8800 Series could allow an unauthenticated, remote attacker to cause an affected phone to reload unexpectedly, resulting in a temporary denial of service (DoS) condition. The vulnerability is due to incomplete error handling when XML data within a SIP packet is parsed. An attacker could exploit this vulnerability by sending a SIP packet that contains a malicious XML payload to an affected phone. A successful exploit could allow the attacker to cause the affected phone to reload unexpectedly, resulting in a temporary DoS condition.
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Analysis
by VulDB Data Team • 09/12/2023
The vulnerability identified as CVE-2019-1635 represents a critical flaw in the Session Initiation Protocol implementation of Cisco IP Phone 7800 and 8800 Series devices. This issue stems from inadequate error handling mechanisms during XML data parsing within SIP packets, creating a pathway for remote exploitation without authentication requirements. The affected phones operate within enterprise communication environments where reliable voice services are paramount, making this vulnerability particularly concerning for organizations dependent on continuous telephony infrastructure. The vulnerability specifically targets the call-handling functionality of these SIP-enabled devices, which form the backbone of many corporate communication networks.
The technical exploitation of this vulnerability occurs through the injection of malicious XML payloads within SIP packets transmitted to affected devices. When the phone's SIP parser encounters malformed or unexpected XML data, the incomplete error handling causes the device to crash and subsequently reload itself. This process results in an immediate disruption of ongoing calls and prevents new call establishment until the device recovers from the restart cycle. The flaw demonstrates poor input validation and exception handling practices that are commonly categorized under CWE-20, which addresses "Improper Input Validation" and CWE-704, which covers "Incorrect Type Conversion or Cast." The vulnerability's exploitation requires minimal privileges and can be executed remotely, aligning with ATT&CK technique T1499.1 for network denial of service attacks.
The operational impact of CVE-2019-1635 extends beyond simple service disruption to potentially compromise business continuity and communication reliability. Organizations relying on these phones for mission-critical communications may experience significant operational downtime, particularly in environments where call availability is essential for customer service, emergency response, or collaborative work processes. The temporary nature of the DoS condition does not mitigate the business impact, as frequent reloads can lead to call abandonment, reduced productivity, and potential financial losses. Network administrators must account for the possibility of cascading failures if multiple phones in a network are simultaneously affected, potentially overwhelming backup systems and creating broader infrastructure issues. The vulnerability's remote exploitation capability means that attackers can target these devices from outside the corporate network, increasing the attack surface and reducing the effectiveness of traditional perimeter security measures.
Mitigation strategies for CVE-2019-1635 should focus on immediate patch deployment from Cisco, which provides firmware updates addressing the XML parsing error handling issues. Organizations should implement network segmentation to isolate affected devices from critical network segments and deploy intrusion detection systems capable of identifying suspicious SIP traffic patterns. The implementation of SIP message filtering and validation rules can help prevent malicious XML payloads from reaching target devices. Additionally, network administrators should establish monitoring protocols to detect unusual phone reload patterns that may indicate exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify any similar issues within the broader network infrastructure. The vulnerability highlights the importance of robust input validation and error handling in telephony systems, emphasizing the need for security-by-design principles in communication device development. Organizations should also consider implementing network access controls and firewall rules that restrict SIP traffic to authorized sources only, reducing the attack surface for such remote exploitation attempts.