CVE-2025-21748 in Linux
Summary
by MITRE • 02/27/2025
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix integer overflows on 32 bit systems
On 32bit systems the addition operations in ipc_msg_alloc() can potentially overflow leading to memory corruption. Add bounds checking using KSMBD_IPC_MAX_PAYLOAD to avoid overflow.
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Analysis
by VulDB Data Team • 05/25/2026
The vulnerability CVE-2025-21748 affects the Linux kernel's ksmbd implementation, specifically targeting 32-bit systems where integer overflow conditions can occur during memory allocation operations. This flaw exists within the ipc_msg_alloc() function which handles inter-process communication messaging for the ksmbd SMB server implementation. The issue represents a classic integer overflow scenario that can lead to memory corruption and potentially arbitrary code execution. The vulnerability is particularly concerning because it affects systems running 32-bit architectures where the address space limitations exacerbate the potential impact of overflow conditions.
The technical flaw manifests when addition operations within ipc_msg_alloc() exceed the maximum representable value for 32-bit integers, causing the calculation to wrap around and produce incorrect memory allocation sizes. This overflow condition occurs during the computation of buffer sizes needed for SMB message processing, where the ksmbd service handles network communication for SMB/CIFS file sharing protocols. The vulnerability specifically impacts systems where the kernel operates in 32-bit mode, as the smaller integer width increases the likelihood of overflow conditions during arithmetic operations that would be less problematic on 64-bit systems. According to CWE classification, this represents a CWE-190: Integer Overflow or Wraparound, which is a well-documented vulnerability pattern in software security.
The operational impact of this vulnerability extends beyond simple memory corruption, as it could enable attackers to manipulate memory layout and potentially execute arbitrary code with kernel privileges. When the integer overflow occurs during memory allocation, it can result in insufficient buffer allocation or incorrect memory mapping, creating opportunities for heap-based attacks or memory corruption that could be exploited to gain elevated privileges. Systems running ksmbd as an SMB server implementation are particularly at risk, especially those that handle multiple concurrent connections or large data transfers where the overflow conditions are more likely to be triggered. The vulnerability aligns with ATT&CK technique T1068: Exploitation for Privilege Escalation, as successful exploitation could lead to kernel-level access.
The resolution for CVE-2025-21748 involves implementing bounds checking using the KSMBD_IPC_MAX_PAYLOAD constant to prevent the addition operations from exceeding safe limits. This mitigation approach directly addresses the root cause by establishing clear boundaries for memory allocation calculations, ensuring that buffer sizes remain within valid ranges regardless of input values. The fix demonstrates proper defensive programming practices by validating all arithmetic operations that could potentially overflow, which aligns with secure coding guidelines recommended by organizations such as the CERT Coordination Center. System administrators should prioritize applying this kernel update across all 32-bit systems running ksmbd services, particularly those serving as SMB file servers in enterprise environments where the vulnerability could be exploited by remote attackers. The mitigation strategy effectively neutralizes the integer overflow condition while maintaining the functionality of the ksmbd SMB implementation.