---
id: CVE-2025-21653
title: 'net_sched: cls_flow: validate TCA_FLOW_RSHIFT attribute'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net_sched: cls_flow: validate TCA_FLOW_RSHIFT attribute

  syzbot found that TCA_FLOW_RSHIFT attribute was not validated.
  Right shitfing a 32bit integer is undefined for …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe <
    9858f4afeb2e59506e714176bd3e135539a3eeec
  - >-
    Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe <
    43658e4a5f2770ad94e93362885ff51c10cf3179
  - >-
    Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe <
    a313d6e6d5f3a631cae5a241c392c28868aa5c5e
  - >-
    Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe <
    2011749ca96460386844dfc7e0fde53ebee96f3c
  - >-
    Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe <
    e54beb9aed2a90dddf4c5d68fcfc9a01f3e40a61
  - >-
    Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe <
    6fde663f7321418996645ee602a473457640542f
  - >-
    Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe <
    a039e54397c6a75b713b9ce7894a62e06956aa92
  - Linux 2.6.25
published: '2025-01-19'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T01:02:49.719Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-21653'
references:
  - url: 'https://git.kernel.org/stable/c/9858f4afeb2e59506e714176bd3e135539a3eeec'
  - url: 'https://git.kernel.org/stable/c/43658e4a5f2770ad94e93362885ff51c10cf3179'
  - url: 'https://git.kernel.org/stable/c/a313d6e6d5f3a631cae5a241c392c28868aa5c5e'
  - url: 'https://git.kernel.org/stable/c/2011749ca96460386844dfc7e0fde53ebee96f3c'
  - url: 'https://git.kernel.org/stable/c/e54beb9aed2a90dddf4c5d68fcfc9a01f3e40a61'
  - url: 'https://git.kernel.org/stable/c/6fde663f7321418996645ee602a473457640542f'
  - url: 'https://git.kernel.org/stable/c/a039e54397c6a75b713b9ce7894a62e06956aa92'
tags:
  - cve.org
epss: 0.00216
epssPercentile: 0.11939
ingestedAt: '2026-10-15T04:46:37.353Z'
---

## Overview

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

net_sched: cls_flow: validate TCA_FLOW_RSHIFT attribute

syzbot found that TCA_FLOW_RSHIFT attribute was not validated.
Right shitfing a 32bit integer is undefined for large shift values.

UBSAN: shift-out-of-bounds in net/sched/cls_flow.c:329:23
shift exponent 9445 is too large for 32-bit type 'u32' (aka 'unsigned int')
CPU: 1 UID: 0 PID: 54 Comm: kworker/u8:3 Not tainted 6.13.0-rc3-syzkaller-00180-g4f619d518db9 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Workqueue: ipv6_addrconf addrconf_dad_work
Call Trace:
 <TASK>
  __dump_stack lib/dump_stack.c:94 [inline]
  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
  ubsan_epilogue lib/ubsan.c:231 [inline]
  __ubsan_handle_shift_out_of_bounds+0x3c8/0x420 lib/ubsan.c:468
  flow_classify+0x24d5/0x25b0 net/sched/cls_flow.c:329
  tc_classify include/net/tc_wrapper.h:197 [inline]
  __tcf_classify net/sched/cls_api.c:1771 [inline]
  tcf_classify+0x420/0x1160 net/sched/cls_api.c:1867
  sfb_classify net/sched/sch_sfb.c:260 [inline]
  sfb_enqueue+0x3ad/0x18b0 net/sched/sch_sfb.c:318
  dev_qdisc_enqueue+0x4b/0x290 net/core/dev.c:3793
  __dev_xmit_skb net/core/dev.c:3889 [inline]
  __dev_queue_xmit+0xf0e/0x3f50 net/core/dev.c:4400
  dev_queue_xmit include/linux/netdevice.h:3168 [inline]
  neigh_hh_output include/net/neighbour.h:523 [inline]
  neigh_output include/net/neighbour.h:537 [inline]
  ip_finish_output2+0xd41/0x1390 net/ipv4/ip_output.c:236
  iptunnel_xmit+0x55d/0x9b0 net/ipv4/ip_tunnel_core.c:82
  udp_tunnel_xmit_skb+0x262/0x3b0 net/ipv4/udp_tunnel_core.c:173
  geneve_xmit_skb drivers/net/geneve.c:916 [inline]
  geneve_xmit+0x21dc/0x2d00 drivers/net/geneve.c:1039
  __netdev_start_xmit include/linux/netdevice.h:5002 [inline]
  netdev_start_xmit include/linux/netdevice.h:5011 [inline]
  xmit_one net/core/dev.c:3590 [inline]
  dev_hard_start_xmit+0x27a/0x7d0 net/core/dev.c:3606
  __dev_queue_xmit+0x1b73/0x3f50 net/core/dev.c:4434

## Affected

- `Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe < 9858f4afeb2e59506e714176bd3e135539a3eeec`
- `Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe < 43658e4a5f2770ad94e93362885ff51c10cf3179`
- `Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe < a313d6e6d5f3a631cae5a241c392c28868aa5c5e`
- `Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe < 2011749ca96460386844dfc7e0fde53ebee96f3c`
- `Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe < e54beb9aed2a90dddf4c5d68fcfc9a01f3e40a61`
- `Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe < 6fde663f7321418996645ee602a473457640542f`
- `Linux >= e5dfb815181fcb186d6080ac3a091eadff2d98fe < a039e54397c6a75b713b9ce7894a62e06956aa92`
- `Linux 2.6.25`

## Remediation

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