CVE-2026-63898 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
USB: serial: mct_u232: fix memory corruption with small endpoint
The driver overrides the maximum transfer size for a specific device which only accepts 16 byte packets for its 32 byte bulk-out endpoint.
Make sure to never increase the maximum transfer size to prevent slab corruption should a malicious device report a smaller endpoint max packet size than expected.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability resides within the Linux kernel's USB serial driver implementation, specifically in the mct_u232 driver module that handles communication with certain USB-to-serial converter devices. This issue represents a memory corruption flaw that occurs when the driver processes data transfers to devices with non-standard endpoint configurations. The core problem manifests when the driver encounters a device that advertises a bulk-out endpoint with a maximum packet size of 16 bytes, despite the endpoint being configured for 32 bytes in the standard USB specification.
The technical flaw stems from improper handling of endpoint transfer size limits within the USB communication stack. When the mct_u232 driver receives information about a device's endpoint characteristics, it incorrectly overrides the maximum transfer size without proper validation of the reported endpoint capabilities. This behavior creates a dangerous condition where the driver assumes a larger transfer capacity than what the physical device can actually handle, leading to buffer overflows and memory corruption within the kernel's slab allocator.
The operational impact of this vulnerability extends beyond simple data transmission errors as it represents a potential path for privilege escalation and system instability. When a malicious device or attacker-controlled USB hardware presents false endpoint size information, the kernel's memory management structures become corrupted through improper buffer handling. This corruption can manifest as kernel panics, system crashes, or potentially allow attackers to execute arbitrary code with kernel privileges.
The vulnerability aligns with CWE-129 Input Validation and CWE-787 Out-of-bounds Write categories from the Common Weakness Enumeration catalog, specifically addressing improper input validation in USB endpoint handling. From an attack perspective, this flaw maps to ATT&CK technique T1059 Command and Scripting Interpreter where attackers could potentially leverage kernel memory corruption to gain elevated privileges. The issue particularly affects systems running Linux kernels with USB serial support where the mct_u232 driver is loaded or used.
Mitigation strategies should focus on implementing proper endpoint size validation within the USB subsystem, ensuring that drivers never increase maximum transfer sizes beyond what the device actually reports. Kernel updates addressing this vulnerability typically include bounds checking mechanisms that verify reported endpoint capabilities against expected values before allowing any transfer size modifications. Administrators should also consider disabling unnecessary USB serial drivers and implementing USB device whitelisting policies to prevent unauthorized devices from connecting to systems. The fix requires careful validation of USB descriptor information, particularly endpoint maximum packet size fields, ensuring that the kernel's USB subsystem maintains proper memory boundaries during data transfers.