CVE-2012-0885 in Asterisk
Summary
by MITRE
chan_sip.c in Asterisk Open Source 1.8.x before 1.8.8.2 and 10.x before 10.0.1, when the res_srtp module is used and media support is improperly configured, allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a crafted SDP message with a crypto attribute and a (1) video or (2) text media type, as demonstrated by CSipSimple.
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Analysis
by VulDB Data Team • 11/29/2021
The vulnerability described in CVE-2012-0885 represents a critical denial of service flaw within the Asterisk Open Source telephony platform that affects versions 1.8.x prior to 1.8.8.2 and 10.x prior to 10.0.1. This issue specifically manifests when the res_srtp module is actively utilized alongside improper media configuration settings, creating a condition where remote attackers can exploit the system through carefully crafted Session Description Protocol messages. The flaw stems from inadequate input validation and error handling within the chan_sip.c component that processes incoming SIP media streams, particularly when handling crypto attributes in SDP payloads. The vulnerability is particularly concerning because it can be triggered through legitimate SIP communication channels without requiring authentication or privileged access, making it highly exploitable in networked environments where Asterisk servers handle incoming calls.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious SDP message containing a crypto attribute within either video or text media types, which triggers a NULL pointer dereference in the Asterisk daemon process. This specific code path in chan_sip.c fails to properly validate the presence and structure of crypto attributes within the SDP payload before attempting to process them, leading to the daemon crashing and subsequently causing a denial of service condition that disrupts legitimate telephony services. The flaw is classified as a NULL pointer dereference under CWE-476, which represents a common class of software vulnerabilities where programs attempt to access memory locations that have not been properly initialized or allocated. This particular implementation issue demonstrates poor defensive programming practices and inadequate error handling mechanisms that should have been present in a production telephony system handling real-time communications.
The operational impact of this vulnerability extends beyond simple service disruption as it can effectively render Asterisk servers unusable for legitimate telephony operations, potentially affecting businesses that rely on VoIP infrastructure for communication. When exploited, the daemon crash creates a cascading effect that may require manual intervention to restore service, including restarting the Asterisk process and potentially disrupting ongoing calls or connections. The vulnerability's exploitation is particularly dangerous in environments where Asterisk serves as a core communication platform for enterprise networks, contact centers, or telephony services, as it can be leveraged by attackers to create service interruptions that may last until system administrators manually intervene. The fact that this vulnerability can be triggered through video or text media types increases its attack surface and makes it more difficult to defend against through simple network filtering approaches.
Organizations using affected versions of Asterisk should prioritize immediate patching to address this vulnerability, as the release of version 1.8.8.2 and 10.0.1 included specific fixes for the NULL pointer dereference issue in the chan_sip.c module. The recommended mitigation strategy involves upgrading to patched versions of Asterisk that contain proper input validation for SDP crypto attributes and enhanced error handling for media stream processing. Additionally, network administrators should consider implementing additional security controls such as SIP message filtering, rate limiting of incoming calls, and monitoring for unusual SDP attribute patterns that may indicate exploitation attempts. This vulnerability aligns with ATT&CK technique T1499.004 for network denial of service attacks and demonstrates the importance of proper input validation in telephony applications. The incident also highlights the need for comprehensive security testing of telephony platforms, particularly those handling real-time media streams where memory corruption vulnerabilities can have severe operational consequences. Organizations should also implement proper logging and alerting mechanisms to detect potential exploitation attempts and maintain regular security updates to protect against similar vulnerabilities in their telephony infrastructure.