CVE-2026-93810 in Linux
Summary
by MITRE • 09/24/2026
In the Linux kernel, the following vulnerability has been resolved:
cachefiles: Fix double fput
Fix a double fput() in error handling in cachefiles_create_tmpfile().
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Analysis
by VulDB Data Team • 09/24/2026
The identified vulnerability resides within the Linux kernel's cache files subsystem, specifically affecting the function responsible for creating temporary files during caching operations. This issue manifests as a reference counting error where the file structure is released more than once through consecutive calls to fput. In the context of operating system kernels, every open file descriptor or file object maintains an internal reference count that tracks how many entities are currently holding a handle to it. When this counter reaches zero, the kernel frees the associated memory and resources. A double free scenario occurs when the release function is invoked while the reference count has already been decremented to zero by a prior call, leading to the deallocation of an object that may have already been reclaimed or repurposed for other uses.
The technical flaw originates in the error handling path of cachefiles_create_tmpfile(). During normal operation, this routine allocates resources and opens files necessary for managing cached data. However, when a failure condition arises during initialization or setup, the code attempts to clean up by releasing previously acquired file handles. Due to incorrect logic flow or missing state checks in the error branch, the cleanup sequence inadvertently calls fput on a file structure that has already been released earlier in the same execution path. This violates the fundamental principle of reference counting integrity and results in undefined behavior within the kernel memory management subsystem.
From an operational perspective, this vulnerability poses significant stability risks to systems relying on the cachefiles mechanism for network filesystem caching, such as NFS over TCP with cache enabled. The immediate consequence is typically a kernel panic or system crash due to corruption of internal data structures like slab caches or inode lists. Attackers who can trigger specific error conditions during temporary file creation might exploit this instability to cause denial of service against the host machine. In more complex exploitation scenarios involving carefully crafted race conditions, such memory corruption could potentially lead to arbitrary code execution if an attacker gains control over the freed memory before it is reallocated for a different purpose with predictable content.
This vulnerability aligns closely with CWE-415 Double Free and CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization of Reference Counting, as it involves improper management of shared resource lifecycles under error conditions. It also relates to ATT&CK technique T1078 Valid Accounts if the vulnerability is leveraged in conjunction with privilege escalation vectors following a system crash or instability event that disrupts security controls. The root cause lies in inadequate state tracking within the kernel module's cleanup routines, where developers failed to ensure idempotency of resource release operations.
Mitigation strategies primarily involve applying vendor-provided patches that correct the control flow logic within cachefiles_create_tmpfile(). System administrators should monitor for updates from their Linux distribution maintainers and apply security advisories promptly. For environments unable to patch immediately, disabling cache files functionality or restricting access to network filesystems that utilize this subsystem can reduce exposure. Additionally, enabling kernel hardening features such as KASAN (Kernel Address Sanitizer) in development builds helps detect such memory errors early during testing phases before deployment to production systems.