CVE-2026-64351 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
net: usb: kalmia: bound RX frame length in kalmia_rx_fixup()
kalmia_rx_fixup() computes usb_packet_length = skb->len - (2 * KALMIA_HEADER_LENGTH) as a u16, guarded only by a pre-loop check that skb->len is at least KALMIA_HEADER_LENGTH, which is 6. A device can deliver a short bulk-IN frame with skb->len in the 6 to 11 range, or leave a short trailing remainder on a later loop iteration. Either case underflows usb_packet_length to about 65530.
That bypasses the usb_packet_length < ether_packet_length truncation path. The device-supplied ether_packet_length, a le16 up to 65535 read from header_start[2], then drives a memcmp() and the following skb_trim() and
skb_pull() past the end of the rx buffer. The rx buffer is hard_mtu * 10, which is 14000 bytes. That is an out of bounds read.
Require both the start and end framing headers to be present before subtracting them, on every loop iteration.
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability exists in the linux kernel's usb networking driver for kalmia devices within the kalmia_rx_fixup() function that processes received usb frames. This flaw represents a classic buffer overread condition stemming from inadequate input validation and length calculation logic. The function computes usb_packet_length as a 16-bit unsigned integer by subtracting twice the kalmia header length from the skb->len value, with only a basic pre-loop check ensuring skb->len is at least 6 bytes. This minimal validation fails to account for edge cases where devices might transmit short bulk-in frames with lengths between 6 and 11 bytes or leave trailing short packets during subsequent loop iterations.
The vulnerability exploitation occurs when these short frames cause underflow in the usb_packet_length calculation, resulting in a value of approximately 65530 instead of the expected smaller packet size. This underflow bypasses the normal truncation path that would typically validate usb_packet_length against ether_packet_length, allowing malicious or faulty device behavior to proceed unchecked. The device-supplied ether_packet_length field, which is a little-endian 16-bit value read from header_start[2] and can reach up to 65535, then drives subsequent memory operations including memcmp() comparisons and buffer manipulation functions like skb_trim() and skb_pull(). These operations attempt to access memory regions beyond the allocated receive buffer boundaries.
The receive buffer size is fixed at hard_mtu * 10, which equals 14000 bytes, making this an out-of-bounds read vulnerability that can potentially expose sensitive kernel memory contents or cause system instability. The flaw stems from CWE-129 Input Validation and CWE-787 Out-of-bounds Write/Read patterns, and aligns with attack techniques documented in the ATT&CK framework under T1059 Command and Scripting Interpreter and T1068 Exploitation for Privilege Escalation. The vulnerability demonstrates poor defensive programming practices where insufficient bounds checking allows malformed input to propagate through critical processing paths. The mitigation strategy requires enforcing that both start and end framing headers must be present before performing any length calculations, implementing proper validation on each loop iteration rather than relying on single pre-loop checks. This approach ensures that all buffer operations remain within allocated memory boundaries regardless of device behavior or packet characteristics.
The vulnerability represents a significant security risk in embedded usb networking scenarios where devices might not strictly adhere to protocol specifications or where malicious actors could exploit this condition to gain unauthorized access to kernel memory regions, potentially leading to privilege escalation or system compromise. The fix addresses the root cause by implementing iterative header validation that prevents the problematic underflow condition and ensures all buffer operations remain within safe boundaries. This remediation aligns with secure coding practices that emphasize defensive programming and comprehensive input validation as primary defenses against buffer overflows and related memory corruption vulnerabilities.