CVE-2026-53036

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.

CVSS v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0014

Probability of exploitation

0.04%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

References

Other References

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

Frequently Asked Questions

What is CVE-2026-53036? +

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. It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2026-53036? +

CVE-2026-53036 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0014, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-53036? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.