CVE-2019-7251 in Open Source
Summary
by MITRE
An Integer Signedness issue (for a return code) in the res_pjsip_sdp_rtp module in Digium Asterisk versions 15.7.1 and earlier and 16.1.1 and earlier allows remote authenticated users to crash Asterisk via a specially crafted SDP protocol violation.
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Analysis
by VulDB Data Team • 05/17/2020
The vulnerability CVE-2019-7251 represents a critical integer signedness issue within the res_pjsip_sdp_rtp module of Digium Asterisk PBX systems. This flaw exists in versions 15.7.1 and earlier, as well as 16.1.1 and earlier, where the software fails to properly validate return code values during SDP (Session Description Protocol) processing. The issue stems from improper handling of signed integer values when processing RTP (Real-time Transport Protocol) session descriptions, creating a condition where maliciously crafted SDP messages can trigger unexpected behavior in the application's memory management routines.
The technical exploitation of this vulnerability occurs through the manipulation of SDP protocol elements that contain return code values which are not properly constrained for signedness. When an authenticated attacker sends a specially crafted SDP message with malformed return code values, the Asterisk system processes these values without adequate bounds checking or type validation. This leads to integer overflow conditions or incorrect memory pointer calculations that ultimately result in application crashes and potential denial of service scenarios. The vulnerability specifically targets the SDP parsing logic within the pjsip stack, which is responsible for handling session negotiation between SIP endpoints.
From an operational perspective, this vulnerability poses significant risks to VoIP infrastructure deployments that rely on Asterisk as their core communication platform. Since the attack requires only authenticated access to the system, it can be exploited by malicious insiders or compromised accounts with legitimate access rights. The impact extends beyond simple service disruption as the crash conditions can potentially lead to system instability, making it difficult to maintain reliable communication services. Organizations running Asterisk versions affected by this vulnerability face the risk of unauthorized service disruption that could affect business continuity and customer communication capabilities. The vulnerability aligns with CWE-191, which specifically addresses integer underflow conditions, and can be categorized under ATT&CK technique T1499.1 for network denial of service attacks.
Mitigation strategies for CVE-2019-7251 should prioritize immediate patching of affected Asterisk installations to versions 15.7.2 and 16.1.2 or later, which contain the necessary code fixes to properly validate return code values during SDP processing. Network administrators should implement additional monitoring and logging of SIP traffic to detect anomalous SDP message patterns that may indicate attempted exploitation. Access controls and authentication mechanisms should be strengthened to limit the attack surface, as the vulnerability requires authenticated access to function. Organizations should also consider implementing intrusion detection systems that can identify and alert on suspicious SDP protocol violations. The fix typically involves adding proper bounds checking and type validation for return code values within the res_pjsip_sdp_rtp module, ensuring that signed integer values are properly constrained to prevent overflow conditions during RTP session processing.