CVE-2025-21947 in Linux
Summary
by MITRE • 04/01/2025
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix type confusion via race condition when using ipc_msg_send_request
req->handle is allocated using ksmbd_acquire_id(&ipc_ida), based on ida_alloc. req->handle from ksmbd_ipc_login_request and FSCTL_PIPE_TRANSCEIVE ioctl can be same and it could lead to type confusion between messages, resulting in access to unexpected parts of memory after an incorrect delivery. ksmbd check type of ipc response but missing add continue to check next ipc reponse.
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Analysis
by VulDB Data Team • 02/01/2026
The vulnerability identified as CVE-2025-21947 resides within the Linux kernel's ksmbd implementation, specifically addressing a critical type confusion issue that emerges through a race condition during ipc_msg_send_request operations. This flaw manifests when the kernel's smb2 server implementation processes inter-process communication messages, creating conditions where memory access patterns become unpredictable and potentially exploitable. The vulnerability operates at the intersection of kernel-level memory management and concurrent access control, representing a sophisticated attack surface that could enable arbitrary code execution or information disclosure.
The technical root cause stems from the improper handling of request identifiers within the ksmbd subsystem. When ksmbd_acquire_id(&ipc_ida) is invoked to allocate req->handle using ida_alloc, the system fails to properly validate or distinguish between different message types that may share identical handle values. This particular implementation flaw allows both ksmbd_ipc_login_request and FSCTL_PIPE_TRANSCEIVE ioctl operations to potentially utilize the same req->handle value, creating a scenario where type confusion occurs between different message structures. The underlying issue demonstrates poor resource management and insufficient validation mechanisms that should prevent such cross-contamination of memory references between distinct operational contexts.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling attackers to manipulate kernel memory structures through carefully crafted IPC requests. When the ksmbd system processes responses, it performs type checking but fails to implement adequate validation loops that would continue examining subsequent responses for consistency. This missing validation step creates a pathway where an attacker could potentially deliver malformed messages that, when processed, result in access to unexpected memory regions. The vulnerability's exploitation potential aligns with attack patterns described in the ATT&CK framework under privilege escalation and defense evasion techniques, particularly targeting kernel-mode execution environments.
This vulnerability corresponds to CWE-121, which addresses stack-based buffer overflow conditions, and CWE-122, which covers heap-based buffer overflow scenarios, though the specific manifestation involves type confusion rather than traditional buffer overflows. The race condition component of this vulnerability aligns with CWE-362, describing concurrent execution issues that can lead to security flaws. Mitigation strategies should focus on implementing proper handle value validation and ensuring that all IPC responses undergo comprehensive type checking before memory access operations occur. Additionally, the system should enforce stricter synchronization mechanisms during handle allocation and deallocation processes to prevent the reuse of identifiers in contexts where type confusion could occur. The fix should include mandatory validation loops that prevent processing of IPC responses until all type consistency checks are completed, aligning with security best practices outlined in the Linux kernel security documentation and industry standards for secure kernel development.