CVE-2018-14622 in libtirpc
Summary
by MITRE
A null-pointer dereference vulnerability was found in libtirpc before version 0.3.3-rc3. The return value of makefd_xprt() was not checked in all instances, which could lead to a crash when the server exhausted the maximum number of available file descriptors. A remote attacker could cause an rpc-based application to crash by flooding it with new connections.
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Analysis
by VulDB Data Team • 05/06/2023
The null-pointer dereference vulnerability identified as CVE-2018-14622 resides within the libtirpc library, a critical component for remote procedure call implementations in Unix-like systems. This flaw specifically affects versions prior to 0.3.3-rc3 and represents a fundamental failure in error handling mechanisms that govern file descriptor management within rpc-based applications. The vulnerability manifests when the makefd_xprt() function fails to return a valid pointer, yet the calling code does not verify this condition before proceeding with subsequent operations. The issue is particularly concerning because it directly impacts the stability and availability of rpc services that rely on libtirpc for their operation, creating a potential denial of service scenario that could be exploited by malicious actors.
The technical implementation of this vulnerability stems from inadequate validation of the makefd_xprt() function return value within the libtirpc codebase. When system resources become exhausted and the maximum number of available file descriptors is reached, the makefd_xprt() function legitimately returns a null pointer to indicate failure. However, the application code fails to check for this null return value before attempting to dereference the pointer, resulting in an immediate crash. This pattern of error handling failure aligns with CWE-476, which specifically addresses null pointer dereference vulnerabilities where applications fail to validate function return values. The flaw demonstrates poor defensive programming practices that are commonly exploited in privilege escalation and denial of service attacks.
From an operational perspective, this vulnerability creates a significant risk for systems that rely heavily on rpc services, particularly those that handle high volumes of concurrent connections. A remote attacker can exploit this weakness by flooding the target server with new rpc connections until the system reaches its file descriptor limit, triggering the null pointer dereference and causing the rpc service to crash. This creates a straightforward denial of service attack vector that requires minimal resources to execute and can effectively disrupt legitimate service availability. The attack scenario maps directly to ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion, making this vulnerability particularly dangerous in production environments where rpc services are critical to system operation.
The impact of this vulnerability extends beyond simple service disruption, as it can potentially be leveraged in more sophisticated attack chains. When rpc services crash due to this vulnerability, they may leave the system in an inconsistent state, potentially exposing other attack surfaces or creating opportunities for privilege escalation. System administrators must consider that a successful exploitation could lead to cascading failures across dependent services that rely on rpc communications. The vulnerability's remediation requires updating to libtirpc version 0.3.3-rc3 or later, which includes proper error handling for the makefd_xprt() function. Additionally, organizations should implement connection limiting mechanisms and monitoring to detect unusual connection patterns that might indicate exploitation attempts, as well as ensure that rpc services are properly configured with appropriate resource limits to minimize the impact of potential exploitation scenarios.