CVE-2018-17159 in FreeBSD
Summary
by MITRE
In FreeBSD before 11.2-STABLE(r340854) and 11.2-RELEASE-p5, the NFS server lacks a bounds check in the READDIRPLUS NFS request. Unprivileged remote users with access to the NFS server can cause a resource exhaustion by forcing the server to allocate an arbitrarily large memory allocation.
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Analysis
by VulDB Data Team • 06/12/2023
The vulnerability identified as CVE-2018-17159 represents a critical bounds checking flaw in the FreeBSD NFS server implementation that affects versions prior to 11.2-STABLE(r340854) and 11.2-RELEASE-p5. This issue specifically manifests in the READDIRPLUS NFS request handling mechanism where the server fails to validate the size parameters provided by remote clients. The absence of proper input validation allows malicious actors to manipulate the request parameters and trigger unintended memory allocation behavior that can lead to system resource exhaustion.
The technical flaw stems from a missing bounds check in the NFS server's handling of directory listing operations. When processing READDIRPLUS requests, the server allocates memory based on client-provided size parameters without proper verification of whether these values fall within reasonable operational limits. This oversight creates a condition where unprivileged remote users can submit malformed requests that instruct the server to allocate memory buffers of arbitrary size, potentially consuming all available system memory resources. The vulnerability operates at the kernel level within the NFS server implementation, making it particularly dangerous as it can be exploited without requiring elevated privileges.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it can lead to complete system instability and denial of service conditions. Remote attackers can leverage this weakness to consume system memory rapidly, potentially causing the system to become unresponsive or crash entirely. The memory allocation behavior can also trigger system paging and swapping operations that further degrade performance, making the system vulnerable to cascading failures. Additionally, the vulnerability affects systems that rely heavily on NFS services, making it particularly dangerous in enterprise environments where network file sharing is prevalent.
From a cybersecurity perspective, this vulnerability aligns with CWE-129, which addresses insufficient validation of length of input buffers, and can be categorized under ATT&CK technique T1499.1 for resource exhaustion. The flaw demonstrates poor input validation practices in kernel-level network services and represents a classic example of how insufficient bounds checking can lead to memory corruption and resource exhaustion attacks. Organizations should prioritize immediate patching of affected FreeBSD systems to address this vulnerability, as it provides a straightforward path for remote attackers to cause system disruption without requiring authentication or elevated privileges. The recommended mitigation involves upgrading to FreeBSD versions 11.2-STABLE(r340854) or later, which contain the necessary bounds checking mechanisms to prevent the arbitrary memory allocation behavior that enables this attack vector.