CVE-2012-3923 in IOS
Summary
by MITRE
The SSLVPN implementation in Cisco IOS 12.4, 15.0, 15.1, and 15.2, when DTLS is not enabled, does not properly handle certain outbound ACL configurations, which allows remote authenticated users to cause a denial of service (device crash) via a session involving a PPP over ATM (PPPoA) interface, aka Bug ID CSCte41827.
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Analysis
by VulDB Data Team • 04/19/2017
The vulnerability identified as CVE-2012-3923 represents a critical denial of service flaw within Cisco IOS software versions 12.4, 15.0, 15.1, and 15.2 that affects SSLVPN implementations. This vulnerability specifically manifests when Datagram Transport Layer Security DTLS is not enabled on the affected devices, creating a scenario where authenticated remote attackers can exploit a flaw in the handling of outbound access control list configurations. The issue occurs during sessions that utilize PPP over ATM interfaces, commonly referred to as PPPoA, which establishes a point-to-point connection over ATM networks. The vulnerability falls under CWE-119, which addresses memory access violations and improper handling of network protocol implementations, making it particularly dangerous as it can be exploited by authenticated users who already possess legitimate access credentials.
The technical mechanism behind this vulnerability involves the improper processing of outbound access control lists when SSLVPN sessions are established through PPPoA interfaces without DTLS protection. When an authenticated user initiates a session that involves these specific network conditions, the IOS software fails to correctly manage the memory structures associated with the access control list processing. This malfunction causes the device to enter an unstable state where system resources become corrupted or improperly managed, ultimately leading to a complete device crash and subsequent denial of service for all network services. The flaw demonstrates a classic example of improper input validation and resource management, as the system does not adequately validate the configuration parameters before processing them during active sessions.
The operational impact of this vulnerability extends beyond simple service disruption as it can affect enterprise networks that rely heavily on SSLVPN connectivity for remote access. Organizations using affected Cisco IOS versions may experience complete network outages when authenticated attackers exploit this flaw, particularly in environments where SSLVPN is the primary method for remote employee access or branch office connectivity. The vulnerability's exploitation requires only authenticated access, which means that insiders or compromised legitimate users could potentially trigger device crashes, making it particularly concerning from a security perspective. Network administrators may find themselves unable to maintain service availability during critical business hours, leading to productivity losses and potential financial impacts. This vulnerability also affects the broader security posture as it provides a vector for attackers to disrupt network operations without requiring advanced exploitation techniques.
Mitigation strategies for CVE-2012-3923 should prioritize immediate software updates to the latest available IOS versions that contain patches addressing this specific flaw. Cisco has released security advisories and patches specifically targeting this vulnerability, which should be implemented as soon as possible in production environments. Network administrators should also consider implementing additional monitoring and alerting mechanisms to detect unusual patterns in SSLVPN sessions that might indicate exploitation attempts. Temporary workarounds could include disabling SSLVPN functionality on affected interfaces until proper patches are deployed, though this approach may impact legitimate business operations. Organizations should also review their access control policies to ensure that only necessary users have access to SSLVPN services, reducing the potential attack surface. From an ATT&CK framework perspective, this vulnerability aligns with techniques related to privilege escalation and denial of service, as it allows authenticated users to escalate their access from legitimate network usage to disruptive system-level operations, potentially enabling further exploitation attempts within the compromised network environment.