CVE-2017-8779 in rpcbind
Summary
by MITRE
rpcbind through 0.2.4, LIBTIRPC through 1.0.1 and 1.0.2-rc through 1.0.2-rc3, and NTIRPC through 1.4.3 do not consider the maximum RPC data size during memory allocation for XDR strings, which allows remote attackers to cause a denial of service (memory consumption with no subsequent free) via a crafted UDP packet to port 111, aka rpcbomb.
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Analysis
by VulDB Data Team • 12/22/2024
The vulnerability identified as CVE-2017-8779 represents a critical memory allocation flaw in RPC (Remote Procedure Call) implementations that affects multiple libraries including rpcbind, LIBTIRPC, and NTIRPC. This vulnerability specifically targets the XDR (External Data Representation) string handling mechanism where the system fails to properly validate or limit the maximum RPC data size during memory allocation processes. The flaw exists in versions of these libraries prior to 0.2.4 for rpcbind, 1.0.1 for LIBTIRPC, and 1.4.3 for NTIRPC, creating a persistent security gap that has affected numerous network services relying on RPC communication protocols. The vulnerability is particularly dangerous because it operates at the core networking layer where RPC services typically listen for incoming requests on port 111, making it a prime target for network-based attacks.
The technical exploitation of this vulnerability occurs through crafted UDP packets sent to port 111, which is the standard port for RPC services. When these malformed packets arrive, the affected libraries do not properly enforce maximum size limits for XDR string data structures during memory allocation. This allows attackers to cause the system to allocate excessive amounts of memory without proper subsequent deallocation, leading to progressive memory consumption that eventually results in denial of service conditions. The flaw operates as a memory exhaustion attack where the system's memory resources are gradually consumed until the service becomes unresponsive or crashes entirely. This type of vulnerability falls under CWE-129, which specifically addresses improper validation of length of inputs to functions, and represents a classic example of insufficient resource management in network services.
The operational impact of CVE-2017-8779 extends beyond simple service disruption to potentially compromise entire network infrastructure when multiple services rely on affected RPC implementations. Systems running vulnerable versions of these libraries become susceptible to memory exhaustion attacks that can be executed remotely without authentication requirements, making them particularly attractive targets for automated exploitation campaigns. The vulnerability affects not only individual hosts but also entire network domains where RPC services are commonly deployed, including NFS (Network File System) servers, NIS (Network Information Service) servers, and various other network services that depend on RPC for inter-process communication. Attackers can leverage this vulnerability to perform sustained denial of service attacks that may require system reboot to restore normal operation, effectively creating a persistent availability threat.
Mitigation strategies for CVE-2017-8779 require immediate patching of all affected libraries and implementations, with particular attention to systems running rpcbind, LIBTIRPC, and NTIRPC versions prior to the fixed releases. Network administrators should implement firewall rules to restrict access to port 111 from trusted networks only, and consider disabling RPC services when they are not actively required. The vulnerability also highlights the importance of implementing proper input validation and resource limits in network services, aligning with ATT&CK technique T1499.004 for resource exhaustion attacks. Organizations should conduct comprehensive inventory audits to identify all systems running vulnerable versions of these libraries and establish monitoring procedures to detect unusual memory consumption patterns that might indicate exploitation attempts. Additionally, implementing intrusion detection systems that can identify malformed UDP packets targeting port 111 will provide early warning capabilities for potential exploitation attempts. The vulnerability serves as a reminder of the critical importance of proper resource management and input validation in network services, particularly those handling external communications where attackers can manipulate data size parameters to cause system instability.