CVE-2017-9372 in Asterisk
Summary
by MITRE
PJSIP, as used in Asterisk Open Source 13.x before 13.15.1 and 14.x before 14.4.1, Certified Asterisk 13.13 before 13.13-cert4, and other products, allows remote attackers to cause a denial of service (buffer overflow and application crash) via a SIP packet with a crafted CSeq header in conjunction with a Via header that lacks a branch parameter.
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Analysis
by VulDB Data Team • 12/26/2020
The vulnerability identified as CVE-2017-9372 represents a critical buffer overflow flaw within PJSIP, a widely-used SIP (Session Initiation Protocol) library that forms the foundation of numerous VoIP implementations including Asterisk Open Source. This vulnerability specifically targets versions of Asterisk prior to 13.15.1 and 14.4.1, as well as Certified Asterisk 13.13 before 13.13-cert4, making it a significant concern for organizations relying on these telephony platforms. The flaw manifests when processing SIP packets containing maliciously crafted CSeq headers combined with Via headers that lack the required branch parameter, creating a condition that can be exploited by remote attackers to disrupt service availability.
The technical implementation of this vulnerability stems from inadequate input validation within the PJSIP library's SIP message parsing mechanism. When a SIP packet arrives with a malformed CSeq header and a Via header missing the branch parameter, the library fails to properly handle the boundary conditions during buffer allocation and data copying operations. This deficiency creates a classic buffer overflow scenario where attacker-controlled data exceeds the allocated memory space, leading to memory corruption and subsequent application instability. The vulnerability operates at the protocol level, making it particularly dangerous as it can be triggered through standard SIP communication channels without requiring authentication or privileged access.
The operational impact of CVE-2017-9372 extends beyond simple service disruption to encompass potential system compromise and business continuity risks. Remote attackers can leverage this vulnerability to execute denial of service attacks against VoIP infrastructure, causing complete service outages that can severely impact communication systems in enterprise environments, call centers, and telephony services. The application crash resulting from this buffer overflow can lead to repeated service restarts, creating cascading failures in interconnected systems. Organizations using affected versions of Asterisk face the risk of unauthorized service disruption, which can result in financial losses, customer dissatisfaction, and potential regulatory compliance issues in environments where continuous communication is mandated.
Mitigation strategies for this vulnerability require immediate patching of affected systems to the recommended versions that contain the necessary code fixes. Organizations should prioritize updating their Asterisk installations to versions 13.15.1 or later for the 13.x series, and 14.4.1 or later for the 14.x series, along with the appropriate certified releases. Network-level defenses should include implementing SIP-specific firewalls and intrusion detection systems that can monitor for suspicious SIP packet patterns and automatically block traffic containing malformed headers. Additionally, administrators should consider implementing rate limiting and connection tracking mechanisms to prevent exploitation attempts. The vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and maps to ATT&CK technique T1499.004 for network denial of service attacks, highlighting the importance of both defensive measures and monitoring capabilities in protecting against such threats.