CVE-2008-2739 in IOS
Summary
by MITRE
The SERVICE.DNS signature engine in the Intrusion Prevention System (IPS) in Cisco IOS 12.3 and 12.4 allows remote attackers to cause a denial of service (device crash or hang) via network traffic that triggers unspecified IPS signatures, a different vulnerability than CVE-2008-1447.
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Analysis
by VulDB Data Team • 05/27/2025
The vulnerability described in CVE-2008-2739 represents a critical denial of service weakness within Cisco's Intrusion Prevention System implementation. This flaw exists specifically within the SERVICE.DNS signature engine component of the IPS functionality in Cisco IOS versions 12.3 and 12.4. The vulnerability allows remote attackers to deliberately trigger device crashes or system hangs by sending specially crafted network traffic that activates unspecified IPS signatures. Unlike CVE-2008-1447 which addressed different aspects of the IPS system, this vulnerability focuses specifically on the DNS signature processing mechanism that governs how the system handles domain name service traffic patterns. The attack vector is particularly concerning because it operates entirely over the network without requiring authentication or physical access to the device, making it exploitable from any remote location with network connectivity to the affected Cisco IOS system.
The technical implementation of this vulnerability stems from improper handling of network traffic within the IPS signature matching process. When the SERVICE.DNS signature engine encounters specific patterns in incoming network packets, the processing logic fails to properly validate or sanitize the input data before attempting signature matching operations. This inadequate input validation leads to memory corruption or stack overflow conditions that ultimately cause the IOS operating system to crash or become unresponsive. The vulnerability manifests when legitimate network traffic containing specific DNS-related patterns triggers the signature engine to process malformed or unexpected data sequences that exceed buffer boundaries or corrupt internal data structures. The root cause aligns with CWE-121, which describes heap-based buffer overflow conditions, and CWE-125, which covers out-of-bounds read conditions that can lead to system instability.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network infrastructure reliability and availability. Organizations relying on Cisco IOS devices for network security enforcement face significant risk of unauthorized denial of service attacks that could render their security infrastructure ineffective. When a device experiences a crash or hang, network traffic flows through the affected system are interrupted, potentially creating security gaps in network protection and forcing network administrators to manually intervene to restore service. The vulnerability's remote exploitability means that attackers can target multiple devices simultaneously across different network segments, making it particularly dangerous for large enterprise networks or service provider infrastructures where multiple Cisco devices may be deployed. This type of attack directly impacts the availability component of the CIA triad and can be leveraged as part of broader network disruption campaigns.
Network security professionals should implement immediate mitigations to protect against exploitation of this vulnerability. The primary recommended approach involves applying the latest Cisco IOS patches and updates that contain fixes for the SERVICE.DNS signature engine processing logic. Organizations should also consider implementing network access controls that limit exposure of vulnerable devices to untrusted networks and establish monitoring protocols to detect unusual traffic patterns that may indicate exploitation attempts. The mitigation strategy should include configuring the IPS system to disable or modify the affected DNS signature rules until proper patches are deployed. From an ATT&CK framework perspective, this vulnerability maps to techniques involving denial of service attacks and system compromise through exploitation of software vulnerabilities. Security teams should also consider implementing intrusion detection rules that can identify and alert on traffic patterns consistent with the exploit conditions, providing early warning capabilities to prevent successful attacks. Additionally, maintaining comprehensive network documentation and implementing regular vulnerability assessment procedures will help ensure rapid identification and remediation of similar vulnerabilities in the future.