CVE-2025-40293 in Linux
Summary
by MITRE • 12/08/2025
In the Linux kernel, the following vulnerability has been resolved:
iommufd: Don't overflow during division for dirty tracking
If pgshift is 63 then BITS_PER_TYPE(*bitmap->bitmap) * pgsize will overflow to 0 and this triggers divide by 0.
In this case the index should just be 0, so reorganize things to divide by shift and avoid hitting any overflows.
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Analysis
by VulDB Data Team • 02/23/2026
The vulnerability identified as CVE-2025-40293 resides within the Linux kernel's iommufd subsystem, specifically addressing a critical arithmetic overflow condition that could lead to system instability. This flaw manifests in the dirty tracking mechanism where improper handling of bit shift operations creates a scenario susceptible to division by zero errors. The issue occurs when the page shift value reaches its maximum permissible limit of 63, triggering mathematical overflow conditions that compromise system integrity.
The technical root cause stems from the manipulation of bitmap data structures within the iommufd driver where the expression BITS_PER_TYPE(bitmap->bitmap) pgsize becomes mathematically invalid when pgshift equals 63. This mathematical overflow results in a value of zero which subsequently causes a division by zero error during the dirty tracking process. The vulnerability represents a classic case of integer overflow that occurs in memory management subsystems where bit manipulation operations fail to account for boundary conditions in their calculations. This type of flaw falls under the CWE-191 category of Integer Underflow/Overflow, specifically manifesting as an arithmetic overflow that leads to undefined behavior.
The operational impact of this vulnerability extends beyond simple system crashes to potentially enable privilege escalation or denial of service conditions within virtualized environments that rely on iommufd for memory management. Systems utilizing Intel IOMMU (Input-Output Memory Management Unit) functionality, particularly those running virtualization workloads, face heightened risk as the iommufd subsystem manages memory mappings for device access. Attackers could potentially exploit this condition to cause system panics or disrupt memory management operations, affecting the stability of virtual machines and containerized applications that depend on proper IOMMU functionality.
Mitigation strategies should focus on implementing proper bounds checking and arithmetic overflow protection within the iommufd subsystem. The recommended fix involves reorganizing the division operations to avoid overflow conditions by dividing by shift values rather than relying on potentially problematic multiplication operations. This approach aligns with the principle of defensive programming and follows ATT&CK technique T1068 which addresses local privilege escalation through kernel vulnerabilities. System administrators should prioritize applying kernel updates that include the patched iommufd implementation, particularly in environments running virtualization platforms or systems requiring robust IOMMU functionality. The fix also emphasizes the importance of proper input validation and boundary condition handling in kernel space operations, which directly relates to security best practices outlined in the CWE-191 standard for integer overflow prevention.