CVE-2026-53394 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
nfsd: avoid leaking pre-allocated openowner on unconfirmed retry race
When find_or_alloc_open_stateowner() encounters an unconfirmed owner, it calls release_openowner() and sets oo = NULL. Control then falls through past the `if (oo)` guard -- which would have freed any pre-allocated `new` -- and unconditionally executes `new = alloc_stateowner(...)`. If `new` was already allocated on a prior iteration, the pointer is silently overwritten and the previous allocation (slab object + owner name buffer) is leaked.
This requires a race: two NFSv4.0 OPEN threads with the same owner string, where a concurrent thread inserts a new unconfirmed owner into the hash between retry iterations. The window is narrow but repeatable under adversarial conditions.
Fix by adding `goto retry` after `oo = NULL` so the already-allocated `new` is reused on the next iteration rather than overwritten.
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Analysis
by VulDB Data Team • 07/19/2026
This vulnerability resides in the linux kernel's nfsd implementation, specifically within the nfs4_open_stateowner management logic. The flaw manifests as a memory leak occurring during the processing of NFSv4.0 OPEN operations when handling concurrent client requests with identical owner strings. The issue stems from improper state management during retry scenarios where the kernel fails to properly handle pre-allocated stateowner objects, creating a condition where allocated memory resources become orphaned and unrecoverable.
The technical root cause involves the find_or_alloc_open_stateowner() function which manages the lifecycle of open stateowners in the nfsd subsystem. When this function encounters an unconfirmed owner during processing, it executes release_openowner() to clean up the existing stateowner but sets the oo pointer to NULL without proper cleanup of any pre-allocated new object from a previous iteration. The subsequent code path fails to check for the presence of a previously allocated new object before proceeding to allocate a fresh one, resulting in an overwrite operation that silently discards the prior allocation and creates a memory leak.
This vulnerability operates through a specific race condition scenario requiring precise timing between multiple threads executing NFSv4.0 OPEN operations. The attack vector involves two concurrent threads processing OPEN requests with identical owner strings while a third thread concurrently inserts a new unconfirmed owner into the hash table between retry iterations. This narrow window of opportunity allows the memory leak to occur consistently under adversarial conditions, making it both repeatable and exploitable by malicious actors who can trigger the specific threading pattern required for the race condition.
The operational impact of this vulnerability extends beyond simple memory consumption issues as it represents a denial-of-service vector that can gradually deplete system resources over time. Each occurrence results in leaked slab objects and owner name buffers that cannot be reclaimed by the kernel's memory management system, potentially leading to system instability or resource exhaustion. The vulnerability aligns with CWE-401: Improper Release of Memory Before Next Use, which specifically addresses memory leaks caused by improper object lifecycle management.
From an attack perspective, this flaw fits within the broader category of resource exhaustion attacks that can be leveraged to create denial-of-service conditions in nfsd services. The ATT&CK framework categorizes such issues under T1499.004: Endpoint Denial of Service - Application Exhaustion, where adversaries exploit application-level memory management flaws to consume system resources and render services unavailable. The vulnerability demonstrates how subtle race condition handling errors can create persistent resource leaks that degrade system performance over time.
The fix implemented addresses the core issue by introducing a proper goto retry mechanism after setting oo = NULL. This ensures that any pre-allocated new object from previous iterations is properly reused rather than overwritten, maintaining the integrity of memory allocation patterns and preventing the silent loss of allocated resources. The solution aligns with secure coding practices for concurrent programming and proper resource management in kernel space operations, ensuring that all allocated objects are either properly utilized or safely released before proceeding to subsequent iterations.
Security practitioners should monitor for this vulnerability in nfsd implementations and ensure proper patching of affected systems. The memory leak characteristics make this particularly concerning in high-availability environments where sustained NFS service availability is critical, as the gradual accumulation of leaked resources can eventually impact system stability and performance. Regular security auditing of kernel components and concurrent programming patterns remains essential to prevent similar issues from emerging in complex network services that handle multiple simultaneous client connections and stateful operations.