CVE-2026-93120 in Linux
Summary
by MITRE • 09/18/2026
In the Linux kernel, the following vulnerability has been resolved:
usb: gadget: configfs: fix out-of-bounds read of qw_sign
os_desc_qw_sign_show() passes OS_STRING_QW_SIGN_LEN as the input length to utf16s_to_utf8s(), but that argument counts UTF-16 code units while OS_STRING_QW_SIGN_LEN (14) is the byte size of qw_sign[].
The array holds only OS_STRING_QW_SIGN_LEN / 2 (7) code units, so the conversion reads up to 7 units (14 bytes) past the end of qw_sign[]
into the following members of struct gadget_info when the stored signature fills the array without a NUL terminator, exposing those bytes through the configfs attribute.
The store path halves the count for its input bound but passes the full byte count as the utf8s_to_utf16s() output limit; use the destination code-unit count in both directions.
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Analysis
by VulDB Data Team • 09/18/2026
A critical out-of-bounds read vulnerability exists within the Linux kernel's USB gadget subsystem, specifically affecting the configfs interface used to configure device descriptors. The flaw is located in the os_desc_qw_sign_show function, which handles reading the OS String qw_sign attribute from user space via sysfs or configfs interfaces. This component is responsible for exposing specific operational system descriptor strings that allow host devices to identify and interact with USB gadgets configured through the kernel's configuration filesystem.
The technical root cause stems from a fundamental misunderstanding of character encoding lengths during string conversion operations. The function passes OS_STRING_QW_SIGN_LEN, which equals fourteen bytes, as the input length parameter to the utf16s_to_utf8s conversion routine. However, this API expects the number of UTF-16 code units rather than byte counts. Since the underlying qw_sign array contains only seven UTF-16 code units totaling fourteen bytes, passing fourteen as the unit count causes the converter to read beyond the allocated buffer boundary. This occurs particularly when the stored signature fills the entire array without a null terminator, leading the kernel to access memory locations immediately following the struct gadget_info member in question.
This memory corruption results in an information disclosure vulnerability where sensitive internal state data from adjacent members of the gadget_info structure is exposed through the configfs attribute interface. An attacker with local access capable of interacting with USB gadget configuration endpoints can exploit this out-of-bounds read to leak kernel memory contents. Such leakage may reveal pointers, flags, or other structural metadata that could facilitate further exploitation attempts against the host system. The vulnerability aligns with CWE-125, which classifies out-of-bounds reads as a distinct category of buffer handling errors where software reads data beyond intended boundaries.
The remediation strategy involves correcting the length calculations for both read and write operations within this subsystem. For the show path, developers must halve the byte count to derive the correct number of UTF-16 code units before passing it to the conversion function. Similarly, the store path requires adjustment where the input bound was previously halfed but the output limit incorrectly used full byte counts instead of destination code-unit counts. Ensuring consistent use of code unit counts in both directions prevents boundary violations during string transformations and maintains memory safety guarantees within the kernel space.
From a threat modeling perspective, this vulnerability represents an opportunity for local privilege escalation or reconnaissance if combined with other weaknesses such as type confusion or heap spraying techniques. It falls under ATT&CK technique T1082, which covers system information discovery via operating system APIs. Security practitioners should apply upstream kernel patches that address these specific length calculation errors in the usb gadget configfs module. Additionally, enabling strict bounds checking and utilizing static analysis tools during development can help detect similar off-by-one or unit conversion mismatches before they reach production environments. Regular auditing of string handling functions is essential to prevent recurrence of such encoding-related buffer overflows.