CVE-2014-3347 in IOS
Summary
by MITRE
Cisco IOS 15.1(4)M2 on Cisco 1800 ISR devices, when the ISDN Basic Rate Interface is enabled, allows remote attackers to cause a denial of service (device hang) by leveraging knowledge of the ISDN phone number to trigger an interrupt timer collision during entropy collection, leading to an invalid state of the hardware encryption module, aka Bug ID CSCul77897.
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Analysis
by VulDB Data Team • 02/11/2022
The vulnerability described in CVE-2014-3347 represents a critical denial of service weakness affecting Cisco IOS software version 15.1(4)M2 running on Cisco 1800 Integrated Services Router devices. This flaw specifically manifests when the ISDN Basic Rate Interface is activated, creating a scenario where remote attackers can exploit the system through knowledge of a specific ISDN phone number to trigger a cascading failure in the device's interrupt handling mechanisms. The vulnerability operates at the intersection of hardware and software components, particularly targeting the hardware encryption module's entropy collection process, which serves as a fundamental security function for cryptographic operations.
The technical execution of this vulnerability involves a sophisticated timing attack that exploits the interaction between the ISDN interface and the device's interrupt timer subsystem. When an attacker provides a valid ISDN phone number, the system enters a state where interrupt timer collisions occur during the entropy collection process, which is typically used to gather random data for cryptographic key generation. This collision results in an invalid state within the hardware encryption module, causing the device to become unresponsive and effectively hang. The vulnerability demonstrates a classic example of how improper resource management and timing considerations in security-critical systems can lead to complete service disruption. The underlying mechanism operates through the device's inability to properly handle concurrent interrupt events during cryptographic operations, creating a race condition that leads to system instability.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the overall security posture of network infrastructure. When a Cisco 1800 ISR device becomes unresponsive due to this vulnerability, it creates a denial of service condition that can affect critical network communications, particularly in environments where ISDN interfaces are used for backup or primary communication paths. The hardware encryption module's invalid state represents a serious concern because it can prevent legitimate cryptographic operations from completing successfully, potentially leaving the device vulnerable to other attacks or rendering security features ineffective. This vulnerability also highlights the importance of proper entropy collection mechanisms in cryptographic systems, as the failure to properly manage random number generation can create cascading failures that affect system stability. The impact is particularly severe in mission-critical environments where network availability is paramount and where the device's encryption capabilities are relied upon for secure communications.
Mitigation strategies for this vulnerability should include immediate deployment of Cisco's recommended security patches and software updates that address the interrupt timer collision issue in the ISDN interface implementation. Network administrators should also consider disabling ISDN Basic Rate Interface functionality on affected devices when it is not actively required, as this represents a fundamental prevention measure that eliminates the attack surface entirely. The implementation of proper monitoring and alerting systems can help detect anomalous behavior in the encryption module's state, providing early warning of potential exploitation attempts. Additionally, organizations should review their network architecture to ensure that critical services are not dependent on devices vulnerable to this type of denial of service attack. This vulnerability aligns with CWE-362, which addresses race conditions in security-critical code paths, and demonstrates characteristics consistent with ATT&CK technique T1499.004 related to network denial of service attacks. The remediation process should also include comprehensive testing of updated firmware to ensure that the fix does not introduce regressions in other device functionalities while maintaining the integrity of cryptographic operations.