CVE-2017-12270 in IOS XR
Summary
by MITRE
A vulnerability in the gRPC code of Cisco IOS XR Software for Cisco Network Convergence System (NCS) 5500 Series Routers could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition when the emsd service stops. The vulnerability is due to the software's inability to process HTTP/2 packets. An attacker could exploit this vulnerability by sending a malformed HTTP/2 frame to the affected device. A successful exploit could allow the attacker to create a DoS condition when the emsd service stops. Cisco Bug IDs: CSCvb99388.
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Analysis
by VulDB Data Team • 01/15/2021
The vulnerability identified as CVE-2017-12270 represents a critical denial of service weakness in Cisco IOS XR Software running on NCS 5500 Series Routers. This flaw specifically targets the gRPC implementation within the network infrastructure, creating a pathway for remote attackers to disrupt critical network services without requiring authentication credentials. The affected emsd service, which handles specific management functions, becomes vulnerable to exploitation when processing malformed HTTP/2 protocol frames, demonstrating a fundamental failure in input validation and protocol handling within the router's software stack. The vulnerability stems from the software's inability to properly parse and process HTTP/2 packets, creating a condition where maliciously crafted frames can trigger unexpected behavior in the system's networking components.
The technical exploitation of this vulnerability occurs through the transmission of specifically crafted malformed HTTP/2 frames to the targeted router. This attack vector leverages the HTTP/2 protocol's complexity and the gRPC implementation's insufficient validation mechanisms to trigger a cascade of failures leading to service disruption. When the emsd service encounters these malformed frames, it fails to properly handle the unexpected input, resulting in the service terminating unexpectedly and causing a denial of service condition. The flaw manifests as a complete service stoppage that affects the router's ability to maintain normal network operations, potentially disrupting critical network convergence services that rely on the emsd functionality for management and control plane operations. This represents a classic example of a protocol handling vulnerability where improper input validation leads to service termination rather than graceful error handling.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network stability and availability in production environments. Network administrators managing Cisco NCS 5500 Series routers face significant risk of unplanned outages when this vulnerability is exploited, particularly in mission-critical infrastructure where continuous network availability is essential. The unauthenticated nature of the attack means that any remote attacker with network access can potentially trigger the DoS condition, making the vulnerability particularly dangerous in exposed network environments. The emsd service failure creates a cascading effect that can impact other dependent services and network functions, potentially leading to broader network degradation beyond the immediate router affected by the attack. This vulnerability affects the operational continuity of network infrastructure and can result in service level agreement violations for organizations relying on these critical network convergence systems.
Mitigation strategies for CVE-2017-12270 should focus on immediate software updates and network segmentation approaches to limit exposure. Cisco has released patches addressing this vulnerability through security advisories, and organizations should prioritize applying these updates to all affected routers. Network administrators should implement firewall rules and access control lists to restrict access to HTTP/2 ports and gRPC endpoints where possible, reducing the attack surface available to potential attackers. Monitoring systems should be enhanced to detect unusual patterns in HTTP/2 traffic that might indicate exploitation attempts, and network telemetry should be configured to alert on emsd service instability or unexpected restarts. The vulnerability aligns with CWE-20, which describes improper input validation, and maps to ATT&CK technique T1499.004 for network disruption attacks. Organizations should also consider implementing network segmentation strategies to isolate critical network convergence systems and reduce the potential impact of successful exploitation attempts. Regular vulnerability assessments and security audits should be conducted to identify similar protocol handling weaknesses in other network infrastructure components.