CVE-2026-74544 is a vulnerability in Linux Kernel
Published on August 15, 2026
net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds
In the Linux kernel, the following vulnerability has been resolved:
net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds
u32_change() copies the user-provided tc_u32_sel.offshift (unsigned char,
0-255) into the kernel knode object without bounds validation. When a
packet later hits u32_classify() with TC_U32_VAROFFSET set, it evaluates
`ntohs(offmask & *data) >> offshift` where the left operand is a 16-bit
value promoted to a 32-bit int. Any offshift >= 32 is undefined behavior
per C11 6.5.7p3, triggerable by an unprivileged user via user/network
namespaces.
UBSAN: shift-out-of-bounds in net/sched/cls_u32.c:236:43
shift exponent 32 is too large for 32-bit type int
Fix this by rejecting offshift >= 16 during filter creation in
u32_change().
Products Associated with CVE-2026-74544
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Affected Versions
Linux:- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 313cb9ffc4101a885d791facf4b5ea3d5e06144d is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below aef96eead2860cbfa371e4471d4f04412213b958 is affected.
- Version 2.6.12 is affected.
- Before 2.6.12 is unaffected.
- Version 7.1.8, <= 7.1.* is unaffected.
- Version 7.2-rc6, <= * is unaffected.