net_sched: Prevent creation of classes with TC_H_ROOT
Priority LOW 35CWE-835Published · Updated
Key facts
- Attack vector
- Local
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Partial Red Hat: 5 without a fix
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat. Impact type from CWE-835.
Summary
In the Linux kernel, the following vulnerability has been resolved: net_sched: Prevent creation of classes with TC_H_ROOT The function qdisc_tree_reduce_backlog() uses TC_H_ROOT as a termination condition when traversing up the qdisc tree to update parent backlog counters. However, if a class is created with classid TC_H_ROOT, the traversal terminates prematurely at this class instead of reaching the actual root qdisc, causing parent statistics to be incorrectly maintained. In case of DRR, this could lead to a crash as reported by Mingi Cho. Prevent the creation of any Qdisc class with classid TC_H_ROOT (0xFFFFFFFF) across all qdisc types, as suggested by Jamal.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00227 13th percentileScored 2026-11-07
Fix Partial Linux (Linux): 5.4.292, 5.10.236, 5.15.180 +5Red Hat: 5 without a fix
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Linux | Linux | 2.6.25 and later | 5.4.292, 5.10.236, 5.15.180, 6.1.132, 6.6.84, 6.12.20, 6.13.8, 6.14 | Patch available | CNA |
- Linux VendorLinux Affected 2.6.25 and later Fixed in 5.4.292, 5.10.236, 5.15.180, 6.1.132, 6.6.84, 6.12.20, 6.13.8, 6.14 Patch available CNA
CPE configurations NVD · 8
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | 2.6.26 to before 5.4.292; 5.5 to before 5.10.236; 5.11 to before 5.15.180; 5.16 to before 6.1.132; 6.2 to before 6.6.84; 6.7 to before 6.12.20; 6.13 to before 6.13.8 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:2.6.25:-:*:*:*:*:*:* | 2.6.25 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:6.14:rc1:*:*:*:*:*:* | 6.14 rc1 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:6.14:rc2:*:*:*:*:*:* | 6.14 rc2 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:6.14:rc3:*:*:*:*:*:* | 6.14 rc3 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:6.14:rc4:*:*:*:*:*:* | 6.14 rc4 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:6.14:rc5:*:*:*:*:*:* | 6.14 rc5 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:6.14:rc6:*:*:*:*:*:* | 6.14 rc6 | Vulnerable | Linux |
- cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* Versions 2.6.26 to before 5.4.292; 5.5 to before 5.10.236; 5.11 to before 5.15.180; 5.16 to before 6.1.132; 6.2 to before 6.6.84; 6.7 to before 6.12.20; 6.13 to before 6.13.8 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:2.6.25:-:*:*:*:*:*:* Versions 2.6.25 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:6.14:rc1:*:*:*:*:*:* Versions 6.14 rc1 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:6.14:rc2:*:*:*:*:*:* Versions 6.14 rc2 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:6.14:rc3:*:*:*:*:*:* Versions 6.14 rc3 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:6.14:rc4:*:*:*:*:*:* Versions 6.14 rc4 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:6.14:rc5:*:*:*:*:*:* Versions 6.14 rc5 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:6.14:rc6:*:*:*:*:*:* Versions 6.14 rc6 Vulnerable ·Linux
Remediation
- Fix · CNA Linux (Linux) Fixed in 5.4.292, 5.10.236, 5.15.180, 6.1.132, 6.6.84, 6.12.20, 6.13.8, 6.14
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 10 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 7 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 8 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 9 | Affected | No fix yet: Fix deferred |
Timeline
- 2026-10-02 Threatist record created from CVE-2025-21971
- 2026-10-03 Alias added: GHSA-37v5-vmq6-f37g
- 2026-10-16 CISA SSVC decision points changed
References
Patch 8
- https://git.kernel.org/stable/c/e05d9938b1b0ac40b6054cc5fa0ccbd9afd5ed4c
- https://git.kernel.org/stable/c/7a82fe67a9f4d7123d8e5ba8f0f0806c28695006
- https://git.kernel.org/stable/c/003d92c91cdb5a64b25a9a74cb8543aac9a8bb48
- https://git.kernel.org/stable/c/e5ee00607bbfc97ef1526ea95b6b2458ac9e7cb7
- https://git.kernel.org/stable/c/78533c4a29ac3aeddce4b481770beaaa4f3bfb67
- https://git.kernel.org/stable/c/5c3ca9cb48b51bd72bf76b8b05e24f3cd53db5e7
- https://git.kernel.org/stable/c/94edfdfb9505ab608e86599d1d1e38c83816fc1c
- https://git.kernel.org/stable/c/0c3057a5a04d07120b3d0ec9c79568fceb9c921e
More Linux Kernel vulnerabilities
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- TI-2026-38352 netfilter: bridge: make ebt_snat ARP rewrite writable KEVCVSS 3.1HIGH 8.8
- TI-2013-05264 The (1) get_user and (2) put_user API functions in the Linux kernel before 3.5.5 on the… KEVCVSS 3.1HIGH 8.8
- TI-2022-00125 Integer overflow in kernel KEVCVSS 3.1HIGH 8.4
- TI-2013-01864 The perf_swevent_init function in kernel/events/core.c in the Linux kernel before 3.8.9… KEVCVSS 3.1HIGH 8.4
- TI-2021-05514 Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACE KEVCVSS 3.1HIGH 8.3
Sources
- CVE-2025-21971 · CVE Program
- CVE-2025-21971 · NVD
- FIRST EPSS
- GHSA-37v5-vmq6-f37g · GitHub Advisory Database · CC BY 4.0
- CVE-2025-21971 · Red Hat security data · CC BY 4.0
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