CVE-2024-47737 in Linux
Summary
by MITRE • 10/21/2024
In the Linux kernel, the following vulnerability has been resolved:
nfsd: call cache_put if xdr_reserve_space returns NULL
If not enough buffer space available, but idmap_lookup has triggered lookup_fn which calls cache_get and returns successfully. Then we missed to call cache_put here which pairs with cache_get.
Reviwed-by: Jeff Layton
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Analysis
by VulDB Data Team • 01/19/2026
The vulnerability identified as CVE-2024-47737 resides within the Linux kernel's Network File System daemon implementation, specifically affecting the nfsd subsystem. This issue represents a memory management flaw that occurs during the processing of NFS requests involving identity mapping operations. The vulnerability manifests when the system attempts to reserve space in XDR (External Data Representation) buffers while handling NFS operations that require mapping user identifiers between different naming schemes. The flaw is particularly significant because it impacts the kernel's ability to properly manage reference counts for cached identity mapping entries, creating potential memory leak scenarios that could degrade system performance over time.
The technical root cause of this vulnerability stems from improper resource management within the nfsd code path that handles identity mapping lookups. When the xdr_reserve_space function fails to allocate sufficient buffer space for processing an NFS request, the system still executes the idmap_lookup function which triggers a lookup_fn callback. This callback successfully calls cache_get to retrieve or create a cache entry, but fails to pair this operation with a corresponding cache_put call when the buffer allocation subsequently fails. This mismatch creates a reference count leak where the cache entry remains allocated in memory even though it should be released, effectively causing a memory leak that accumulates over time with repeated NFS operations.
The operational impact of this vulnerability extends beyond simple memory consumption issues, potentially affecting system stability and performance under sustained NFS workloads. Attackers could exploit this condition to cause gradual memory exhaustion on systems running NFS servers, leading to reduced system responsiveness or even system crashes in extreme cases. The vulnerability is particularly concerning in environments where NFS services are heavily utilized, such as large enterprise file servers or storage clusters where continuous NFS operations are common. The memory leak could be exacerbated by repeated NFS requests that trigger the problematic code path, making the system progressively less stable over time.
Mitigation strategies for CVE-2024-47737 primarily involve applying the kernel patch that corrects the resource management issue by ensuring that cache_put is called whenever cache_get is invoked, regardless of subsequent buffer allocation outcomes. System administrators should prioritize updating their Linux kernel installations to versions containing this fix, particularly in production environments where NFS services are critical to operations. Additionally, monitoring system memory usage and NFS service performance can help detect potential exploitation attempts or the accumulation of memory leaks. The fix aligns with established security practices for preventing resource leak vulnerabilities and follows the principles outlined in CWE-401, which addresses improper release of memory, and relates to the broader category of memory management issues that can be exploited to cause denial of service conditions. Organizations should also consider implementing automated patch management processes to ensure timely deployment of kernel security updates, as this vulnerability could potentially be leveraged by adversaries to perform persistent resource exhaustion attacks against NFS services.