CVE-2026-90055
Low risk· EPSS 11%Exploitation Probability (EPSS)
Low risk11th percentile - higher than 11% of all known CVEs
Summary
A bug in the Linux kernel's usbatm (USB ATM) module was found where the ci_range fields vpi_bits and vci_bits were initialized to ATM_CI_MAX (-1). These values are used as bit shift counts in net/atm/common.c, causing undefined behavior (shift-out-of-bounds) and UBSAN warnings. The fix sets vpi_bits to 8 and vci_bits to 16.
Risk Assessment
The vulnerability can lead to undefined kernel behavior, potential system crashes, or errors in ATM interface operation. Exploitation requires access to ATM socket operations, limiting the attack vector, but in environments with USB ATM devices it may cause system instability.
Recommendation
Update the Linux kernel to a version containing the fix for CVE-2026-90055. If updating is not possible, consider restricting access to USB ATM devices or disabling unused kernel modules.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: usb: atm: usbatm: fix invalid ci_range initialization syzbot reported a shift-out-of-bounds in __vcc_connect(): UBSAN: shift-out-of-bounds in net/atm/common.c:382:32 shift exponent -1 is negative CPU: 0 UID: 0 PID: 5987 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026 Call Trace: <TASK> dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 ubsan_epilogue+0xa/0x30 lib/ubsan.c:233 __ubsan_handle_shift_out_of_bounds+0x36d/0x400 lib/ubsan.c:494 __vcc_connect+0x14b4/0x19c0 net/atm/common.c:382 vcc_connect+0x328/0x8f0 net/atm/common.c:498 pvc_bind+0x272/0x380 net/atm/pvc.c:52 __sys_bind+0x2e3/0x410 net/socket.c:1976 __x64_sys_bind+0x7a/0x90 net/socket.c:1979 ... ATM device ci_range fields (vpi_bits and vci_bits) represent the number of bits supported for VPI and VCI addressing on the device. net/atm/common.c directly uses these fields as bit shift counts: vpi >> dev->ci_range.vpi_bits vci >> dev->ci_range.vci_bits 1 << vcc->dev->ci_range.vpi_bits 1 << vcc->dev->ci_range.vci_bits usbatm_atm_init() sets ci_range.vpi_bits and ci_range.vci_bits to ATM_CI_MAX (-1), which is defined in <uapi/linux/atmdev.h> as a sentinel value for userspace ATM_SETCIRANGE requests, not a valid bit count. Shifting by -1 is undefined behavior and triggers UBSAN warnings. ATM UNI cell headers allow up to 8 bits for VPI (0..255) and 16 bits for VCI (0..65535). Initialize vpi_bits to 8 and vci_bits to 16, as done by solos-pci.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

