CVE-2026-64559 in Linux
Summary
by MITRE • 07/29/2026
In the Linux kernel, the following vulnerability has been resolved:
s390/pkey: Check length in PKEY_VERIFYPROTK ioctl
Explicitly check the buffer length request structure provided by user-space and fail, if it exceeds the buffer size.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 07/30/2026
The vulnerability in question pertains to a security flaw within the Linux kernel's s390 architecture implementation specifically related to the protection key verification functionality. This issue manifests in the PKEY_VERIFYPROTK ioctl command which is designed to verify protection keys within the system. The core problem lies in the absence of proper validation for buffer length parameters provided by user-space applications, creating a potential avenue for memory corruption or privilege escalation attacks.
The technical flaw stems from insufficient input validation within the kernel's ioctl handler for protection key operations. When user-space applications invoke the PKEY_VERIFYPROTK ioctl command, they provide a request structure containing buffer length information that should be validated against the actual allocated buffer size. Without explicit checks, malicious or malformed requests can cause buffer overflows or underflows, potentially allowing attackers to overwrite adjacent memory regions or manipulate kernel data structures. This vulnerability directly relates to CWE-129 Input Validation and CWE-787 Out-of-bounds Write, as it fails to properly validate the bounds of user-provided buffer parameters.
The operational impact of this vulnerability is significant within mainframe environments utilizing s390 architecture where protection keys are critical for memory management and security isolation. An attacker with access to execute the ioctl command could potentially exploit this flaw to escalate privileges, corrupt kernel memory, or gain unauthorized access to protected system resources. The vulnerability affects systems running Linux kernels that support the s390 architecture and implement protection key functionality, making it particularly concerning for enterprise environments relying on IBM mainframe systems or virtualized s390 environments.
Mitigation strategies should focus on implementing proper buffer length validation within the kernel's ioctl handler for PKEY_VERIFYPROTK operations. The fix requires explicit checking of user-provided buffer structure lengths against allocated buffer sizes before processing any data, ensuring that requests exceeding the valid buffer boundaries are rejected with appropriate error codes. System administrators should ensure all affected systems are updated with patched kernel versions that include this validation mechanism. Additionally, monitoring for unusual ioctl command patterns and implementing proper access controls for protection key operations can help detect potential exploitation attempts.
This vulnerability aligns with ATT&CK technique T1068, which covers Local Privilege Escalation through kernel exploits, and may also relate to T1547.006 for privilege escalation via kernel modules or system calls. The fix should be deployed as part of broader security hardening measures for s390-based systems, including regular kernel updates, proper access controls, and monitoring for anomalous system call patterns that could indicate exploitation attempts. Organizations using Linux on IBM mainframe systems should prioritize this patch to maintain the integrity and security of their critical infrastructure components.