CVE-2026-63899 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
USB: serial: mxuport: fix memory corruption with small endpoint
Make sure that the bulk-out endpoint max packet size is at least eight bytes to avoid user-controlled slab corruption should a malicious device report a smaller size.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability in question affects the Linux kernel's USB serial driver implementation, specifically within the mxuport module responsible for handling USB serial communications. This issue represents a classic memory safety flaw that arises from inadequate input validation during device enumeration and endpoint configuration. The vulnerability stems from the kernel's failure to properly validate the maximum packet size reported by USB devices during the bulk-out endpoint configuration process, creating a potential pathway for memory corruption through user-controlled data manipulation.
The technical flaw manifests when a malicious USB device presents an unexpectedly small maximum packet size value for its bulk-out endpoint during enumeration. According to industry standards such as CWE-129, this vulnerability falls under improper input validation where the kernel accepts untrusted data without sufficient bounds checking. The mxuport driver does not enforce a minimum threshold of eight bytes for the bulk-out endpoint max packet size, allowing devices to report values that are insufficient for proper buffer management. When the kernel attempts to process data through these malformed endpoints, it can lead to slab corruption in the kernel's memory management system, as documented in the Linux kernel security documentation and referenced by various security frameworks.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling privilege escalation attacks and system stability issues within kernel space. Attackers who can physically access or connect malicious USB devices to target systems can exploit this weakness to corrupt kernel memory structures, potentially leading to denial of service conditions or more severe compromise scenarios. The vulnerability affects systems running Linux kernels that include the mxuport driver implementation, particularly those supporting USB serial communication protocols where endpoint configuration validation is insufficient. This type of flaw aligns with ATT&CK technique T1059.006 for kernel-level exploitation and represents a significant concern for embedded systems and IoT devices that rely heavily on USB serial communications.
Mitigation strategies should focus on implementing proper input validation at the device enumeration stage, enforcing minimum packet size requirements for USB endpoints, and ensuring robust buffer management practices throughout the kernel's USB subsystem. System administrators should update to kernel versions that include patches addressing this specific vulnerability, typically found in recent stable releases of the Linux kernel distribution. The fix involves adding explicit validation checks that verify bulk-out endpoint max packet sizes against minimum required thresholds before proceeding with endpoint configuration, effectively preventing malicious devices from manipulating kernel memory structures through crafted USB device descriptors. Additionally, organizations should implement USB device whitelisting policies and disable unnecessary USB serial functionality in environments where physical security cannot be guaranteed.