CVE-2025-21653

What it is

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

At a glance

Exploitability

Can be exploited locally on the machine with a low-privilege account. High risk of service disruption.

Exploit odds

0.2% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2025-01-19 11:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 08:43 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.2% in the next 30 days (EPSS).
• Severity: 5.5 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2025-01-19 11:15 UTC

Last modified

2026-06-17 08:43 UTC

Exploit probability

0.2% · EPSS, next 30 days

Record status

Modified

Affected

• Linux Kernel < 5.4.290
• Linux Kernel < 5.10.234
• Linux Kernel < 5.15.177
• Linux Kernel < 6.1.125
• Linux Kernel < 6.6.72
• Linux Kernel < 6.12.10
• Linux Kernel 6.13

Attack profile CVSS 3.1 · 5.5

Attack vector

Local

Complexity

Low

Privileges needed

Low

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2025-21653.md and follow it. Check whether this project is affected by CVE-2025-21653. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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