CVE-2019-1909 in IOS XR
Summary
by MITRE
A vulnerability in the implementation of Border Gateway Protocol (BGP) functionality in Cisco IOS XR Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected system. The vulnerability is due to incorrect processing of certain BGP update messages. An attacker could exploit this vulnerability by sending BGP update messages that include a specific set of attributes to be processed by an affected system. A successful exploit could allow the attacker to cause the BGP process to restart unexpectedly, resulting in a DoS condition. The Cisco implementation of BGP accepts incoming BGP traffic from explicitly defined peers only. To exploit this vulnerability, the malicious BGP update message would need to come from a configured, valid BGP peer or would need to be injected by the attacker into the victim's BGP network on an existing, valid TCP connection to a BGP peer.
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Analysis
by VulDB Data Team • 10/18/2023
The vulnerability identified as CVE-2019-1909 represents a critical denial of service weakness within Cisco IOS XR Software's Border Gateway Protocol implementation. This flaw specifically targets the processing mechanisms of BGP update messages, which form the backbone of internet routing communications between autonomous systems. The vulnerability stems from inadequate validation and handling of certain BGP attributes during message processing, creating a pathway for malicious actors to disrupt network operations. The affected Cisco IOS XR Software versions exhibit improper state management when encountering malformed BGP update messages containing specific attribute combinations, leading to unexpected process termination.
The technical exploitation of this vulnerability requires an attacker to craft and transmit carefully constructed BGP update messages that trigger the flawed processing logic within the IOS XR software. The attack vector operates through the existing BGP peer relationships, as the system only accepts traffic from explicitly configured peers. This means that attackers must either establish a legitimate BGP peer relationship with the target device or inject malicious traffic into an existing valid TCP connection to a configured BGP peer. The vulnerability does not require authentication credentials, making it particularly dangerous as it can be exploited remotely without prior access to the system. The specific attributes that trigger the flaw are not publicly disclosed in the CVE description, but they represent a carefully constructed set that causes the BGP process to crash and restart unexpectedly.
The operational impact of this vulnerability extends beyond simple service disruption, as it can severely compromise network stability and availability. When the BGP process restarts due to the vulnerability, it causes temporary loss of routing information and can result in network partitions or complete routing failures within the affected autonomous system. The cascading effects of such an attack can be substantial, as BGP is fundamental to internet connectivity and routing decisions. Network operators may experience extended downtime while the system recovers from the process restart, potentially leading to service interruptions for numerous downstream networks that depend on the affected router's routing decisions. The vulnerability essentially provides an attacker with a mechanism to cause deliberate disruption of internet routing infrastructure, which can have widespread implications for network reliability and business continuity.
Mitigation strategies for CVE-2019-1909 should focus on both immediate defensive measures and long-term architectural improvements. Cisco recommends implementing access control lists to filter incoming BGP traffic and restricting BGP peer relationships to only trusted networks. Network administrators should also apply the relevant security patches and software updates provided by Cisco to address the underlying implementation flaw. Additionally, implementing BGP monitoring and anomaly detection systems can help identify unusual BGP update patterns that may indicate exploitation attempts. The vulnerability aligns with CWE-248, which addresses "Uncaught Exception" in software implementations, and represents a classic example of how improper error handling can lead to denial of service conditions. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 for network denial of service attacks and T1566 for social engineering techniques that may be used to establish initial access to BGP peer relationships. Organizations should also consider implementing BGP security extensions such as Resource Public Key Infrastructure and BGPsec to provide additional protection against malicious BGP updates and reduce the attack surface for similar vulnerabilities.