---
id: CVE-2026-90078
title: >-
  In the Linux kernel, the following vulnerability has been resolved:


  net/sched: act_skbmod: fix length calculations and avoid invalid header
  warnings


  syzbot reported a warning in skb_network_header_len() triggered

  by tcf_skbmod_act():


  …
summary: >-
  In the Linux kernel, the following vulnerability has been resolved:


  net/sched: act_skbmod: fix length calculations and avoid invalid header
  warnings


  syzbot reported a warning in skb_network_header_len() triggered

  by tcf_skbmod_act():


  …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 56af5e749f20c3a540310c207dcc373f4f09156e <
    985a37781ade19061400100c2ba0f43979dd4d63
  - >-
    Linux >= 56af5e749f20c3a540310c207dcc373f4f09156e <
    d896843d8d925f0adbba319020595cfb1a7bcd57
  - >-
    Linux >= 56af5e749f20c3a540310c207dcc373f4f09156e <
    0675cff3c2924eb9b80d9dd250cf56a1140af157
  - >-
    Linux >= 56af5e749f20c3a540310c207dcc373f4f09156e <
    e8a2027b7e686784a69b2dfcee841d779919f313
  - >-
    Linux >= 56af5e749f20c3a540310c207dcc373f4f09156e <
    1719865b20b22c88d2a55e922eff5ca31b0841f6
  - >-
    Linux >= 56af5e749f20c3a540310c207dcc373f4f09156e <
    62126464f3a6159c0a3dd89e196ba65bfeb0afc6
  - >-
    Linux >= 56af5e749f20c3a540310c207dcc373f4f09156e <
    81d0d1e64f30d9989c829c0953cd6e6c68d9c5fb
  - Linux 5.15
published: '2026-09-17'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T17:16:57.057'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-90078'
references:
  - url: 'https://git.kernel.org/stable/c/0675cff3c2924eb9b80d9dd250cf56a1140af157'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/1719865b20b22c88d2a55e922eff5ca31b0841f6'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/62126464f3a6159c0a3dd89e196ba65bfeb0afc6'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/81d0d1e64f30d9989c829c0953cd6e6c68d9c5fb'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/985a37781ade19061400100c2ba0f43979dd4d63'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/d896843d8d925f0adbba319020595cfb1a7bcd57'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/e8a2027b7e686784a69b2dfcee841d779919f313'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-17T16:21:47.896Z'
epss: 0.00206
epssPercentile: 0.10943
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

net/sched: act_skbmod: fix length calculations and avoid invalid header warnings

syzbot reported a warning in skb_network_header_len() triggered
by tcf_skbmod_act():

  !skb_transport_header_was_set(skb)
  WARNING: CPU: 0 PID: 14949 at include/linux/skbuff.h:3243 skb_network_header_len include/linux/skbuff.h:3243 [inline]
  WARNING: CPU: 0 PID: 14949 at net/sched/act_skbmod.c:55 tcf_skbmod_act+0xfe8/0x1810 net/sched/act_skbmod.c:55

There are a few issues in tcf_skbmod_act():

1. Calling skb_network_header_len() assumes skb->transport_header is set,
   which is not guaranteed when tcf_skbmod_act() runs at TC ingress.
2. Unconditionally calling skb_mac_header_len() at the beginning of
   tcf_skbmod_act() triggers a warning on L3 devices (e.g. TUN) where the
   MAC header is unset, evaluating to an underflowed garbage length.
3. On TC ingress, skb->data points to the network header. Adding the MAC
   header length to the IP header length causes skb_ensure_writable() to
   request more bytes than the actual IP packet length, dropping valid
   short packets (e.g. 28-byte UDP/IPv4 packets).

Fix these by:
- Using skb_network_offset(skb) + sizeof(struct iphdr/ipv6hdr) for
  SKBMOD_F_ECN so that the required length is correctly calculated on
  both ingress (offset == 0) and egress (offset == mac_len).
- Setting max_edit_len to ETH_HLEN for Ethernet header modifications
  after validating ARPHRD_ETHER.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.