CVE-2025-22039 in Linux
Summary
by MITRE • 04/16/2025
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix overflow in dacloffset bounds check
The dacloffset field was originally typed as int and used in an unchecked addition, which could overflow and bypass the existing bounds check in both smb_check_perm_dacl() and smb_inherit_dacl().
This could result in out-of-bounds memory access and a kernel crash when dereferencing the DACL pointer.
This patch converts dacloffset to unsigned int and uses check_add_overflow() to validate access to the DACL.
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Analysis
by VulDB Data Team • 02/15/2026
The vulnerability identified as CVE-2025-22039 resides within the Linux kernel's ksmbd implementation, specifically addressing a critical integer overflow condition that compromises memory safety and system stability. This flaw affects the handling of DACL (Discretionary Access Control List) offset calculations during SMB (Server Message Block) protocol operations, creating a pathway for potential exploitation that could lead to system crashes or unauthorized access to kernel memory regions.
The technical root cause stems from the improper handling of the dacloffset field which was originally declared as a signed integer type. This design decision proved problematic when the field was used in unchecked arithmetic operations, particularly addition operations that could result in integer overflow conditions. The vulnerability manifests when the addition of the dacloffset value to another memory address exceeds the maximum representable value for a signed integer, causing the value to wrap around to a negative number or an unexpectedly large positive value. This overflow bypasses the intended bounds checking mechanisms that were designed to prevent out-of-bounds memory access.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable privilege escalation and arbitrary code execution within kernel space. When the overflow occurs, the bounds check in smb_check_perm_dacl() and smb_inherit_dacl() functions fails to properly validate memory access, allowing the kernel to attempt to dereference a DACL pointer at an invalid memory location. This results in a kernel crash through a page fault or memory corruption, which can be exploited by malicious actors to either cause denial of service attacks or potentially gain elevated privileges within the system.
The fix implemented in this patch addresses the vulnerability by converting the dacloffset field from a signed integer to an unsigned integer type, which eliminates the possibility of negative overflow conditions that were enabling the bypass. Additionally, the patch incorporates check_add_overflow() function calls to properly validate arithmetic operations before they are executed, ensuring that the addition of dacloffset values does not exceed safe limits. This approach aligns with security best practices for preventing integer overflow vulnerabilities and follows the principles outlined in CWE-190, which specifically addresses integer overflow and underflow conditions. The mitigation strategy also reflects recommendations from the ATT&CK framework's privilege escalation techniques, where such kernel-level vulnerabilities are commonly exploited to gain elevated system privileges.
The resolution demonstrates proper defensive programming practices by implementing comprehensive input validation and arithmetic overflow detection mechanisms. The patch ensures that all memory access operations involving the DACL offset are properly validated against known safe bounds, preventing the exploitation of arithmetic overflow conditions that could otherwise lead to memory corruption. This vulnerability serves as a critical reminder of the importance of proper integer type selection and arithmetic validation in kernel space operations, where such flaws can have catastrophic consequences for system security and stability. The fix represents a fundamental improvement in kernel memory safety and contributes to the overall robustness of the Linux kernel's SMB implementation against sophisticated exploitation attempts.