CVE-2025-21653 | net_sched: cls_flow: validate TCA_FLOW_RSHIFT attribute

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

Published: 2025-01-19 Last update: 2026-05-12 Assigner: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-21653 is rated Low Risk (25.2/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.03%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2025-21653

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-02-27 0.05% 0.03% -0.02%
2 2025-11-04 0.05% 0.05% +0.00%
3 2025-10-17 — 0.05% —

Full EPSS history (6 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-21653

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.5 3.1 MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 3.6 [email protected]

Weakness enumeration for CVE-2025-21653

GitHub Security Advisory for CVE-2025-21653

GHSA-478m-w5gm-f3cr · Severity: medium — In the Linux kernel, the following vulnerability has been resolved: net_sched: cls_flow:...

OS Trackers for CVE-2025-21653

vendor priority summary link
debian not yet assigned CVE-2025-21653 not yet assigned priority: Debian including 2 source packages (linux, linux-6.1), 6 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 6. https://security-tracker.debian.org/tracker/CVE-2025-21653
redhat medium — https://access.redhat.com/security/cve/CVE-2025-21653
suse medium CVE-2025-21653 severity moderate: SUSE including 422 source package names (2.1.3-4.43:kernel-default-base-6.4.0-24.1.21.4, 2.1.3-6.5:kernel-default-6.4.0-25.1, …), 687 product×package rows across 126 product lines (Container suse/sl-micro/6.0/base-os-container, Container suse/sl-micro/6.0/kvm-os-container, … (126 product lines)): Fixed 435, Known Affected 231, Known Not Affected 21. https://www.suse.com/security/cve/CVE-2025-21653/
ubuntu medium CVE-2025-21653 medium priority: Ubuntu including 158 source packages (linux, linux-allwinner-5.19, …), 1551 status rows across 10 suites (bionic, focal, jammy, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 1145, released 190, ignored 151, not-affected 45, needed 20. https://ubuntu.com/security/CVE-2025-21653

Affected software / configurations for CVE-2025-21653

Vendor Product Version Raw CPE
linux linux_kernel >= 2.6.25, < 5.4.290 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.5, < 5.10.234 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.11, < 5.15.177 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.16, < 6.1.125 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.2, < 6.6.72 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.7, < 6.12.10 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel 6.13 cpe:2.3:o:linux:linux_kernel:6.13:rc1:*:*:*:*:*:*
linux linux_kernel 6.13 cpe:2.3:o:linux:linux_kernel:6.13:rc2:*:*:*:*:*:*
linux linux_kernel 6.13 cpe:2.3:o:linux:linux_kernel:6.13:rc3:*:*:*:*:*:*
linux linux_kernel 6.13 cpe:2.3:o:linux:linux_kernel:6.13:rc4:*:*:*:*:*:*
linux linux_kernel 6.13 cpe:2.3:o:linux:linux_kernel:6.13:rc5:*:*:*:*:*:*
linux linux_kernel 6.13 cpe:2.3:o:linux:linux_kernel:6.13:rc6:*:*:*:*:*:*

References for CVE-2025-21653

URL Tags
https://git.kernel.org/stable/c/2011749ca96460386844dfc7e0fde53ebee96f3c Patch
https://git.kernel.org/stable/c/43658e4a5f2770ad94e93362885ff51c10cf3179 Patch
https://git.kernel.org/stable/c/6fde663f7321418996645ee602a473457640542f Patch
https://git.kernel.org/stable/c/9858f4afeb2e59506e714176bd3e135539a3eeec Patch
https://git.kernel.org/stable/c/a039e54397c6a75b713b9ce7894a62e06956aa92 Patch
https://git.kernel.org/stable/c/a313d6e6d5f3a631cae5a241c392c28868aa5c5e Patch
https://git.kernel.org/stable/c/e54beb9aed2a90dddf4c5d68fcfc9a01f3e40a61 Patch
https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html
https://lists.debian.org/debian-lts-announce/2025/03/msg00002.html
https://cert-portal.siemens.com/productcert/html/ssa-265688.html
https://cert-portal.siemens.com/productcert/html/ssa-503939.html
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