CVE-2025-21971: net_sched: Prevent creation of classes with TC_H_ROOT
Vulnerability summary
CVE-2025-21971 is a high (CVSS 7.8) Loop with Unreachable Exit Condition vulnerability in linux. EPSS estimates a 0.23% chance of exploitation in the next 30 days, higher than 13.5% of scored vulnerabilities.
Not severe (CVSS 7.8, local access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 118 · Related 113Showing 100 of 119.
Timeline
- 01-04-2025PublishedVulnerability first disclosed.
- 15-10-2026Last modifiedVulnerability information updated.
Description
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.
CVSS metrics
5 scores · 4 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated7.8HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- OSV · DebianEcosystem advisory · calculated5.5MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:HDiffers
- NVDNIST5.5MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:HDiffers
EPSS trend
Probability
0.23%
Chance of exploitation in the next 30 days
Percentile
14%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.22% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Known conditions: local access, low-privilege account, no user interaction (CVSS vector). Other conditions: not stated in public data.
Ubuntu136 products
- linuxAll versions (No fix recorded) | < 4.4.0-268.302 | < 4.15.0-237.249 | < 5.4.0-216.236 | < 5.15.0-140.150 | < 6.8.0-60.63
- linux-allwinner-5.19All versions (No fix recorded)
- linux-aws< 4.4.0-1143.149 | < 4.4.0-1181.196 | < 4.15.0-1180.193 | < 5.4.0-1146.156 | < 5.15.0-1084.91 | < 6.8.0-1029.31
- linux-aws-5.0All versions (No fix recorded)
- linux-aws-5.11All versions (No fix recorded)
Linux2 products
- linux≥ 066a3b5b2346febf9a655b444567b7138e3bb939, < e05d9938b1b0ac40b6054cc5fa0ccbd9afd5ed4c | ≥ 066a3b5b2346febf9a655b444567b7138e3bb939, < 7a82fe67a9f4d7123d8e5ba8f0f0806c28695006 | ≥ 066a3b5b2346febf9a655b444567b7138e3bb939, < 003d92c91cdb5a64b25a9a74cb8543aac9a8bb48 | ≥ 066a3b5b2346febf9a655b444567b7138e3bb939, < e5ee00607bbfc97ef1526ea95b6b2458ac9e7cb7 | ≥ 066a3b5b2346febf9a655b444567b7138e3bb939, < 78533c4a29ac3aeddce4b481770beaaa4f3bfb67 | ≥ 066a3b5b2346febf9a655b444567b7138e3bb939, < 5c3ca9cb48b51bd72bf76b8b05e24f3cd53db5e7 | ≥ 066a3b5b2346febf9a655b444567b7138e3bb939, < 94edfdfb9505ab608e86599d1d1e38c83816fc1c | ≥ 066a3b5b2346febf9a655b444567b7138e3bb939, < 0c3057a5a04d07120b3d0ec9c79568fceb9c921e | 2.6.25
- linux_kernel≥ 2.6.26, < 5.4.292 | ≥ 5.5, < 5.10.236 | ≥ 5.11, < 5.15.180 | ≥ 5.16, < 6.1.132 | ≥ 6.2, < 6.6.84 | ≥ 6.7, < 6.12.20 | ≥ 6.13, < 6.13.8 | 2.6.25 | 6.14:rc1 | 6.14:rc2 | 6.14:rc3 | 6.14:rc4 | 6.14:rc5 | 6.14:rc6
Debian1 product
- linux< 6.1.133-1 | < 6.12.20-1
3 vendors · 139 products
