CVE-2026-93210 in Linux
Summary
by MITRE • 09/24/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: client: harden DFS cache against invalid target hints
Currently, get_tgt_name() returns ERR_PTR(-ENOENT) when ce->tgthint is NULL, and dfs_cache_noreq_update_tgthint() assumes ce->tgthint is always valid.
In preparation for clearing ce->tgthint in free_tgts(), harden callers of get_tgt_name() against ERR_PTR results and harden dfs_cache_noreq_update_tgthint() against NULL pointer dereferences.
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Analysis
by VulDB Data Team • 09/24/2026
The Linux kernel's Server Message Block client implementation contains a logic flaw within the Distributed File System cache handling mechanisms that can lead to null pointer dereference vulnerabilities. This issue specifically affects the interaction between target hint management and the DFS cache update routines, where assumptions about data validity are not consistently enforced across all code paths. The vulnerability arises from an inconsistency in how the ce->tgthint field is handled during different phases of the client's operation lifecycle, particularly when transitioning between active caching states and cleanup procedures.
The core technical flaw lies in the mismatched expectations regarding pointer validity within two key functions: get_tgt_name() and dfs_cache_noreq_update_tgthint(). The function get_tgt_name() correctly returns an error pointer with the value ERR_PTR(-ENOENT) when ce->tgthint is NULL, indicating that no target hint is available. However, the routine dfs_cache_noreq_update_tgthint() operates under the implicit assumption that ce->tgthint always points to a valid memory location. This assumption becomes dangerous during the execution of free_tgts(), where ce->tgthint is explicitly cleared or set to NULL as part of resource cleanup. If dfs_cache_noreq_update_tgthint() is invoked after this clearing operation but before subsequent validation checks, it attempts to dereference a null pointer, leading to a kernel panic or system crash.
This vulnerability represents an improper input handling scenario where the software fails to validate assumptions about internal state consistency. From a classification perspective, this aligns with CWE-476: NULL Pointer Dereference, as the code path allows for the access of memory through a null pointer due to inadequate checks on data structure integrity. Furthermore, in the context of attack patterns, this relates to ATT&CK technique T1059.008: Command and Scripting Interpreter via Kernel Modules or internal system processes if an attacker can trigger specific race conditions or state transitions that force the execution path into the vulnerable code segment before proper validation occurs. While typically resulting in denial of service through kernel panic rather than arbitrary code execution, such flaws can potentially be leveraged for local privilege escalation depending on the surrounding context and memory layout protections enabled on the target system.
The operational impact of this vulnerability is primarily a stability issue affecting systems running affected versions of the Linux kernel with SMB client capabilities enabled. An attacker with local access could potentially trigger conditions that cause the DFS cache update routine to execute while ce->tgthint is null, resulting in an immediate crash of the operating system. This denial of service disrupts network file sharing services and requires a full reboot to restore functionality. In environments where availability is critical, such as enterprise file servers or cloud infrastructure relying on SMB-based storage protocols, this flaw poses a significant risk to operational continuity.
To mitigate this vulnerability, it is essential to apply the latest kernel updates provided by your distribution vendor that include the specific patch for hardening DFS cache operations against invalid target hints. Administrators should ensure that all systems utilizing the Linux SMB client are updated to versions where get_tgt_name() callers properly check for ERR_PTR results and dfs_cache_noreq_update_tgthint() includes explicit null checks before dereferencing ce->tgthint. Additionally, implementing strict kernel hardening parameters such as KASLR and stack canaries can reduce the exploitability of any potential follow-on attacks derived from this initial denial-of-service condition. Regular monitoring for system logs indicating oops or panic messages related to SMB client operations is recommended to detect any attempted exploitation in real-time environments until patches are fully deployed.