CVE-2018-5381 in BGP Daemon
Summary
by MITRE
The Quagga BGP daemon (bgpd) prior to version 1.2.3 has a bug in its parsing of "Capabilities" in BGP OPEN messages, in the bgp_packet.c:bgp_capability_msg_parse function. The parser can enter an infinite loop on invalid capabilities if a Multi-Protocol capability does not have a recognized AFI/SAFI, causing a denial of service.
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Analysis
by VulDB Data Team • 01/21/2025
The vulnerability identified as CVE-2018-5381 affects the Quagga BGP daemon version 1.2.2 and earlier, specifically within the bgp_capability_msg_parse function located in bgp_packet.c. This issue represents a critical denial of service vulnerability that exploits a flaw in the BGP OPEN message capability parsing mechanism. The Quagga routing software serves as a widely deployed implementation of routing protocols including BGP, OSPF, and RIP, making this vulnerability particularly significant for network infrastructure security. When a BGP peer sends an OPEN message containing a Multi-Protocol capability with an unrecognized AFI/SAFI combination, the parsing logic fails to properly handle the malformed data structure.
The technical flaw manifests as an infinite loop condition within the capability parsing routine, where the daemon continuously processes the malformed capability data without proper termination conditions. This occurs because the parser does not adequately validate the AFI/SAFI values or implement proper bounds checking when encountering unknown capability types. The vulnerability is classified under CWE-835, which deals with loops that can never terminate, and specifically relates to improper handling of input validation in network protocol implementations. The parser's failure to detect malformed capabilities leads to resource exhaustion and daemon unresponsiveness, effectively rendering the BGP service unavailable to legitimate network peers.
The operational impact of this vulnerability extends beyond simple service disruption, as it can compromise entire network routing domains that depend on BGP for path selection and route advertisement. Network administrators managing Quagga-based routers face potential cascading failures where a single malicious or misconfigured peer can bring down routing services across multiple network segments. This vulnerability particularly affects network infrastructure operators who rely on BGP for inter-domain routing, as it can be exploited through various attack vectors including malicious BGP peers, misconfigured network equipment, or even compromised routing peers. The infinite loop condition consumes CPU resources continuously and can persist until manual intervention or system reboot occurs, making it a persistent threat to network availability.
Mitigation strategies for CVE-2018-5381 include immediate upgrade to Quagga version 1.2.3 or later, which contains the patched capability parsing logic. Network administrators should also implement BGP session filtering and capability validation as part of their security configuration, utilizing access control lists to restrict incoming BGP connections from untrusted peers. The ATT&CK framework categorizes this vulnerability under T1499.004 for Network Denial of Service, emphasizing the need for proper input validation and robust error handling in network protocol implementations. Additional defensive measures include monitoring BGP session stability, implementing automated alerting for unusual CPU utilization patterns, and maintaining comprehensive network segmentation to limit the scope of potential attacks. Organizations should also consider implementing BGP security extensions such as BGPsec or RPKI validation to provide additional protection layers against malformed routing advertisements.