net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds
CVE-2026-74544 · published 15 Aug 2026
How serious is it
- Severity: high, CVSS score 7.8 out of 10.
- No exploit prediction (EPSS) score yet.
- Not on the CISA list of exploited vulnerabilities.
- No public exploit in Exploit-DB.
Is your app affected by CVE-2026-74544?
Paste this prompt into Claude Code, Cursor or any AI coding tool: it runs a free Shippable scan of your project and fixes what it finds. Built with Lovable, Bolt or v0? Scan your live app. Or upload your package file.
Who is affected
- Linux Linux: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 724c8edbacf1259988829cb9967f751222121d8a, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 006a4598da9a6b02e0ddc3ca5042b97224774364, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 9990cac513e8b191de2ee589051ea7ebf3cee940, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 to < 313cb9ffc4101a885d791facf4b5ea3d5e06144d
- Linux Linux: 2.6.12
How to check
- Find out whether you run the affected product and which version, then compare it with the versions above.
How to fix
Copies a prompt for Claude Code, Cursor or Codex that asks it to check whether you run this product.
- Apply the vendor's update or mitigation from the references below. If there is none yet, limit exposure of the affected service until there is.
- If a vulnerable version was live, check your logs and rotate the secrets that server could read.
The advisory
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().
Check your whole app
Dependencies are only half of it. Free and read-only: before you push, run npx shippable-dev scan localhost:3000 in your project folder, no account needed. For your live app, you prove it's yours with a one-line tag first.
References
- git.kernel.org/stable/c/724c8edbacf1259988829cb9967f751222121d8a
- git.kernel.org/stable/c/006a4598da9a6b02e0ddc3ca5042b97224774364
- git.kernel.org/stable/c/9990cac513e8b191de2ee589051ea7ebf3cee940
- git.kernel.org/stable/c/313cb9ffc4101a885d791facf4b5ea3d5e06144d
- git.kernel.org/stable/c/aef96eead2860cbfa371e4471d4f04412213b958
Merged from CVE List. Last updated 25 Oct 2026. All vulnerabilities · RSS · JSON