CVE-2026-64487 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: caiaq: fix out-of-bounds read in the Traktor Kontrol S4 input parser
snd_usb_caiaq_tks4_dispatch() decodes the Traktor Kontrol S4 input stream in fixed 16-byte (TKS4_MSGBLOCK_SIZE) message blocks. On every iteration it advances buf and subtracts the block size while looping on "while (len)".
len is urb->actual_length. That value is supplied by the device and is not guaranteed to be a multiple of 16. When a final short block leaves len between 1 and 15, the loop runs once more, reads up to buf[15], and
then does "len -= TKS4_MSGBLOCK_SIZE". As len is unsigned this underflows to a huge value. The loop then keeps iterating and walking buf far past the end of the 512-byte ep4_in_buf, reading out of bounds until a bogus block id happens to be hit.
Iterate only while a full message block is available. This stops the unsigned underflow and silently drops any trailing partial block, which carries no complete control value anyway.
The sibling endpoint-4 parsers are not affected. The Traktor Kontrol X1 and Maschine arms in snd_usb_caiaq_ep4_reply_dispatch() floor urb->actual_length before dispatching.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 07/26/2026
The vulnerability resides in the Linux kernel's ALSA subsystem specifically within the caiaq USB audio driver module that handles devices from Native Instruments including the Traktor Kontrol S4 controller. This flaw manifests as an out-of-bounds read condition in the snd_usb_caiaq_tks4_dispatch() function which processes input streams from the USB endpoint 4 interface of these devices. The function operates by parsing incoming data in fixed 16-byte message blocks known as TKS4_MSGBLOCK_SIZE, a standard size for communication with the Traktor Kontrol S4 hardware. When processing USB requests, the driver relies on urb->actual_length to determine how much data is available in the buffer, but this value is entirely determined by the physical device and may not align perfectly with the expected block boundaries.
The technical execution of this vulnerability occurs through an improper loop condition that fails to validate whether sufficient data remains for a complete message block. The while (len) loop continues processing even when len contains a value between 1 and 15 bytes, representing a partial final block that does not constitute a complete 16-byte message. During this final iteration, the code reads up to buf[15] which is valid, but then performs len -= TKS4_MSGBLOCK_SIZE where len is an unsigned integer type. This mathematical operation causes an unsigned underflow, transforming the small remaining length value into an extremely large positive number that continues the loop execution far beyond the allocated 512-byte ep4_in_buf buffer boundaries.
The operational impact of this vulnerability extends beyond simple data corruption as it allows for potential memory access violations and information disclosure through out-of-bounds reads. The loop continues iterating through memory locations past the legitimate buffer limits until it encounters what appears to be a valid block identifier, potentially causing unpredictable behavior in the audio driver or providing attackers with access to adjacent memory regions. This vulnerability directly relates to CWE-129 Input Validation and Verification and CWE-787 Out-of-bounds Read as identified by the Common Weakness Enumeration catalog. The flaw also aligns with ATT&CK technique T1059 Command and Scripting Interpreter where malicious actors could potentially exploit such buffer overflows to execute arbitrary code or escalate privileges within the kernel space.
The mitigation strategy implemented in the fix involves modifying the loop condition to ensure that processing only occurs when a complete message block is available. This approach prevents the unsigned integer underflow by checking whether len meets the minimum requirement for a full block before proceeding with any parsing operations. The solution gracefully handles partial blocks by silently discarding them rather than attempting to process incomplete data, which aligns with defensive programming practices and security by design principles. Additionally, this fix demonstrates the importance of proper boundary checking in USB device driver implementations where device-supplied data must be carefully validated against expected buffer constraints.
The vulnerability affects only the specific Traktor Kontrol S4 input parser implementation while leaving other similar drivers unaffected, including the sibling endpoint-4 parsers used for devices like the Traktor Kontrol X1 and Maschine. These alternative parsers implement a different approach by flooring urb->actual_length before dispatching to their respective handlers, effectively preventing the same type of underflow condition from occurring. This difference in implementation highlights the importance of consistent security practices across similar code paths within kernel subsystems and demonstrates how seemingly minor variations in input validation can significantly impact overall system security posture. The fix represents a targeted approach that addresses the root cause rather than merely patching symptoms, maintaining backward compatibility while eliminating the potential for memory corruption attacks through proper bounds checking mechanisms.