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.
Use CWE-399, Cisco vendor hub and Ip Conference Phone 7832 Firmware product page to widen CVE-2019-1635 into its surrounding weakness, vendor, and product context.
Compare it with CVE-2020-3111, CVE-2021-1379 and CVE-2019-1684 for nearby disclosures in the same product family. Additional editorial context is available in The Weekly Cybersecurity Brief: January 30th, 2026.