CVE-2019-0055 in Junos
Summary
by MITRE
A vulnerability in the SIP ALG packet processing service of Juniper Networks Junos OS allows an attacker to cause a Denial of Service (DoS) to the device by sending specific types of valid SIP traffic to the device. In this case, the flowd process crashes and generates a core dump while processing SIP ALG traffic. Continued receipt of these valid SIP packets will result in a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS: 12.3X48 versions prior to 12.3X48-D61, 12.3X48-D65 on SRX Series; 15.1X49 versions prior to 15.1X49-D130 on SRX Series; 17.3 versions prior to 17.3R3 on SRX Series; 17.4 versions prior to 17.4R2 on SRX Series.
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Analysis
by VulDB Data Team • 09/29/2020
The vulnerability described in CVE-2019-0055 represents a critical denial of service weakness within the Session Initiation Protocol Application Layer Gateway functionality of Juniper Networks Junos OS operating systems. This flaw specifically targets the flowd process responsible for handling SIP ALG traffic, creating a condition where legitimate SIP packets can be exploited to trigger system crashes and subsequent service disruption. The issue manifests when the device processes certain valid SIP traffic patterns that cause the flowd daemon to terminate unexpectedly, generating core dump files that indicate the system has encountered an unrecoverable error condition. The vulnerability impacts multiple versions of Junos OS across different release branches, particularly affecting SRX Series devices that rely on SIP ALG functionality for voice and video traffic handling.
The technical exploitation of this vulnerability occurs through carefully crafted SIP packets that trigger a buffer overflow or memory corruption condition within the flowd process during packet processing. When the SIP ALG service encounters these specific packet sequences, it fails to properly validate or handle the incoming traffic, leading to an abrupt termination of the process. The root cause of this behavior can be classified under CWE-121, which describes heap-based buffer overflow conditions, or CWE-125, which addresses out-of-bounds read vulnerabilities. The flowd process, which normally maintains connection tracking and flow state information for SIP traffic, becomes vulnerable to malformed packet processing that causes memory corruption. This memory corruption ultimately leads to a segmentation fault that terminates the process and results in the generation of core dump files, indicating the system has encountered an unrecoverable error.
The operational impact of this vulnerability extends beyond simple service disruption to create sustained denial of service conditions that can severely impact network infrastructure reliability. Network administrators who deploy SRX Series devices with SIP ALG enabled become vulnerable to attacks that can cause continuous system instability, requiring manual intervention to restore service functionality. The sustained nature of the DoS condition means that simply stopping the malicious traffic does not resolve the issue, as the device must be manually restarted or rebooted to clear the corrupted process state. This vulnerability affects enterprise voice and video communication systems that depend on SIP ALG functionality for proper NAT traversal and media stream handling, potentially disrupting critical business communications. The attack vector is particularly concerning because it requires only valid SIP traffic to exploit, meaning that legitimate users or automated systems sending normal SIP packets can inadvertently trigger the vulnerability.
Organizations affected by this vulnerability should immediately implement mitigation strategies that include applying the relevant security patches provided by Juniper Networks. The patched versions mentioned in the CVE description (12.3X48-D61, 12.3X48-D65, 15.1X49-D130, 17.3R3, and 17.4R2) contain fixes that properly validate SIP packet processing and prevent the memory corruption conditions that lead to the flowd process crash. Network security teams should also consider implementing traffic filtering rules that can identify and block suspicious SIP packet patterns, though this approach requires careful configuration to avoid disrupting legitimate voice services. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique for network denial of service attacks, specifically targeting the availability of network infrastructure services. Additionally, the vulnerability demonstrates characteristics of T1566.001 for social engineering through valid traffic patterns, as attackers can leverage legitimate SIP protocols to exploit the system. Organizations should also consider implementing monitoring solutions that can detect the generation of core dump files and process crashes as early warning indicators of potential exploitation attempts.