CVE-2011-1624 in IOS
Summary
by MITRE
Cisco IOS 12.2(58)SE, when a login banner is configured, allows remote attackers to cause a denial of service (device reload) by establishing two SSH2 sessions, aka Bug ID CSCto62631.
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Analysis
by VulDB Data Team • 03/30/2017
Cisco IOS version 12.2(58)SE contains a critical vulnerability that affects devices configured with login banners, creating a remote denial of service condition through SSH2 protocol exploitation. This vulnerability specifically manifests when an attacker establishes two concurrent SSH2 sessions to a vulnerable device, triggering an unexpected device reload that results in complete service interruption. The flaw exists within the IOS operating system's handling of authentication banners during SSH connections, where the system fails to properly manage concurrent session states when banner display is enabled.
The technical root cause of CVE-2011-1624 stems from improper state management within the SSH2 implementation of Cisco IOS, particularly when processing login banners. When two SSH2 sessions are initiated simultaneously with banner configuration active, the system encounters a memory management issue that leads to a kernel panic and subsequent device reload. This behavior represents a classic buffer over-read condition combined with improper resource cleanup, where the device's secure shell service does not properly handle concurrent access to banner display resources. The vulnerability aligns with CWE-129, which addresses improper validation of length parameters, and CWE-125, concerning out-of-bounds read conditions that can lead to system instability.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited remotely without authentication requirements, making it particularly dangerous in network environments where SSH access is permitted. Network administrators face significant challenges in mitigating this issue since the attack can be executed from any location with network connectivity to the affected device, potentially leading to extended downtime for critical network infrastructure. The vulnerability affects Cisco IOS versions up to and including 12.2(58)SE, impacting a wide range of network devices including routers and switches that rely on IOS for operation, creating widespread potential for service disruption across enterprise and service provider networks.
Organizations should implement immediate mitigations including applying the appropriate Cisco IOS software patches that address the SSH2 session handling and banner display logic, or alternatively disabling SSH2 banner functionality until a patch can be deployed. Network segmentation strategies should be employed to limit exposure of vulnerable devices to untrusted networks, while monitoring systems should be configured to detect unusual SSH connection patterns that may indicate exploitation attempts. The vulnerability demonstrates the importance of proper session management in network infrastructure software and aligns with ATT&CK technique T1499.004 for network denial of service attacks, highlighting the need for robust input validation and resource management in critical network services. Organizations should also consider implementing intrusion detection systems that can identify the specific patterns associated with this exploitation method, as well as maintaining detailed logs of SSH session activity for forensic analysis.