CVE-2025-38430 in Linux
Summary
by MITRE • 07/25/2025
In the Linux kernel, the following vulnerability has been resolved:
nfsd: nfsd4_spo_must_allow() must check this is a v4 compound request
If the request being processed is not a v4 compound request, then examining the cstate can have undefined results.
This patch adds a check that the rpc procedure being executed (rq_procinfo) is the NFSPROC4_COMPOUND procedure.
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Analysis
by VulDB Data Team • 01/03/2026
The vulnerability CVE-2025-38430 resides within the Linux kernel's Network File System version 4 server implementation, specifically affecting the nfsd4_spo_must_allow() function. This issue represents a critical flaw in the kernel's NFS server component that could potentially allow unauthorized access or privilege escalation. The vulnerability stems from insufficient validation of request types before processing compound requests, creating a potential security bypass opportunity. The flaw impacts systems running Linux kernels that implement NFS version 4 server functionality, particularly those serving NFS shares to remote clients. Attackers could exploit this weakness to manipulate the NFS server's behavior during compound request processing, potentially leading to unauthorized data access or system compromise.
The technical root cause of this vulnerability lies in the nfsd4_spo_must_allow() function's failure to properly validate that incoming requests are indeed compound requests before examining the client state. When processing NFS version 4 requests, the system must distinguish between different request types to ensure proper authorization checks occur. The function incorrectly assumes all requests being processed are compound requests, but this assumption fails when other request types are received. This oversight results in undefined behavior when examining client state information, as the function's logic was designed specifically for compound request processing. The vulnerability manifests when the kernel's RPC procedure information indicates a non-compound request type, yet the authorization checking code proceeds as if it were processing a compound request, leading to potential security policy violations.
The operational impact of this vulnerability extends beyond simple authorization bypasses, potentially enabling attackers to escalate privileges or access restricted resources within NFS-managed filesystems. Systems utilizing NFS version 4 server functionality, particularly those in enterprise environments where file sharing and remote access are common, face significant risk from this flaw. The vulnerability affects the integrity of the NFS security model by allowing improper state examination during request processing, which could lead to unauthorized file access or modification. This issue is particularly concerning in multi-user environments where NFS servers serve multiple clients with varying access levels, as it could allow lower-privileged users to potentially access resources they should not be authorized to reach. The vulnerability's exploitation requires knowledge of the NFS protocol and the ability to craft specific requests, making it somewhat specialized but still potentially dangerous in environments with insufficient network segmentation.
Mitigation strategies for CVE-2025-38430 should focus on applying the official kernel patch that introduces the required check for NFSPROC4_COMPOUND procedure validation. System administrators must ensure all affected Linux systems receive the appropriate kernel updates, particularly those running NFS version 4 servers in production environments. Network segmentation and firewall rules should be implemented to limit access to NFS services to only trusted networks and hosts, reducing the attack surface. Monitoring for unusual NFS traffic patterns or unauthorized access attempts can help detect potential exploitation attempts. The fix aligns with security best practices outlined in the Common Weakness Enumeration framework, specifically addressing CWE-254 as a security feature weakness in access control mechanisms. Additionally, organizations should consider implementing the ATT&CK framework's privilege escalation techniques to better understand and protect against potential exploitation paths. Regular security audits of NFS server configurations and access controls should be conducted to ensure proper implementation of security policies and prevent similar vulnerabilities from emerging in other components of the system.