CVE-2025-21738 in Linux
Summary
by MITRE • 02/27/2025
In the Linux kernel, the following vulnerability has been resolved:
ata: libata-sff: Ensure that we cannot write outside the allocated buffer
reveliofuzzing reported that a SCSI_IOCTL_SEND_COMMAND ioctl with out_len set to 0xd42, SCSI command set to ATA_16 PASS-THROUGH, ATA command set to ATA_NOP, and protocol set to ATA_PROT_PIO, can cause ata_pio_sector() to write outside the allocated buffer, overwriting random memory.
While a ATA device is supposed to abort a ATA_NOP command, there does seem to be a bug either in libata-sff or QEMU, where either this status is not set, or the status is cleared before read by ata_sff_hsm_move(). Anyway, that is most likely a separate bug.
Looking at __atapi_pio_bytes(), it already has a safety check to ensure that __atapi_pio_bytes() cannot write outside the allocated buffer.
Add a similar check to ata_pio_sector(), such that also ata_pio_sector() cannot write outside the allocated buffer.
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Analysis
by VulDB Data Team • 05/25/2026
The vulnerability identified as CVE-2025-21738 represents a critical buffer overflow flaw within the Linux kernel's libata-sff subsystem that specifically affects ATA device communication handling. This issue manifests when processing SCSI_IOCTL_SEND_COMMAND ioctls with particular parameter combinations that create a scenario where the ata_pio_sector() function can write beyond the bounds of allocated memory buffers. The flaw arises from insufficient input validation and boundary checking within the kernel's ATA command processing pipeline, potentially enabling arbitrary memory corruption that could be exploited by malicious actors to gain unauthorized system access or cause system instability.
The technical implementation of this vulnerability involves a specific sequence of ioctl parameters that trigger the buffer overflow condition. When a SCSI_IOCTL_SEND_COMMAND ioctl is issued with out_len set to 0xd42, a SCSI command set to ATA_16 PASS-THROUGH, an ATA command set to ATA_NOP, and a protocol set to ATA_PROT_PIO, the ata_pio_sector() function executes without proper buffer boundary validation. The vulnerability stems from the fact that while the ata_pio_sector() function lacks the safety checks present in __atapi_pio_bytes(), which already implements proper buffer boundary enforcement, the ata_pio_sector() function fails to validate that write operations remain within allocated buffer boundaries. This discrepancy creates a potential path for attackers to overwrite arbitrary memory locations, particularly when the ATA_NOP command status is not properly maintained or cleared before being read by ata_sff_hsm_move().
The operational impact of this vulnerability extends beyond simple memory corruption, as it represents a potential attack vector that could be leveraged for privilege escalation or denial of service conditions within Linux systems utilizing ATA devices. The flaw affects systems running Linux kernels that incorporate the libata-sff subsystem, particularly those handling SCSI commands through ATA pass-through mechanisms. The vulnerability's exploitation potential is heightened by the fact that it can occur through legitimate ioctl interfaces, making it difficult to distinguish between normal system operations and malicious activity. System administrators and security professionals must consider the implications of this vulnerability when assessing kernel security configurations, as it could enable attackers to corrupt critical kernel memory structures or potentially execute arbitrary code with kernel privileges.
The remediation approach for this vulnerability follows established security practices by implementing defensive programming techniques similar to those already employed in related functions within the same codebase. The solution involves adding boundary checks to the ata_pio_sector() function that mirror the existing safety mechanisms present in __atapi_pio_bytes(), ensuring consistent buffer validation across all ATA I/O operations. This approach aligns with CWE-121, which addresses stack-based buffer overflow conditions, and follows the principle of least privilege by preventing unauthorized memory access patterns. The fix demonstrates adherence to the principle of input validation and boundary checking, which is fundamental to preventing buffer overflow vulnerabilities and aligns with ATT&CK technique T1059.005 for command and scripting interpreter usage, as the vulnerability could potentially be exploited through command injection vectors. Organizations should implement kernel updates containing this fix promptly, as the vulnerability's exploitation potential increases with system exposure time and the presence of vulnerable ATA device interfaces. The vulnerability's resolution through code-level defensive programming reinforces the importance of consistent security practices across all kernel subsystems and demonstrates the critical role of thorough code review processes in identifying and mitigating memory safety issues in operating system components.