NVD / CVE Program· CNA Linux

CVE-2025-21700: net: sched: Disallow replacing of child qdisc from one parent to another

Noroxi assessment

Priority: Monitor (action score 31/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.23% (FIRST EPSS).
Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
Fixed version: Linux Linux 38646749d6e12f9d80a08d21ca39f0beca20230d, 46c59ec33ec98aba20c15117630cae43a01404cc, 73c7e1d6898ccbeee126194dcc05f58b8a795e70; cbl2 kernel 5.15.176.3-3 on CBL Mariner 2.0 5.15.180.1-1; cbl2 kernel 5.15.176.3-3 on CBL-Mariner 2.0 5.15.180.1-1.

Low priority for now. Upgrade to Linux Linux 38646749d6e12f9d80a08d21ca39f0beca20230d, 46c59ec33ec98aba20c15117630cae43a01404cc, 73c7e1d6898ccbeee126194dcc05f58b8a795e70; cbl2 kernel 5.15.176.3-3 on CBL Mariner 2.0 5.15.180.1-1; cbl2 kernel 5.15.176.3-3 on CBL-Mariner 2.0 5.15.180.1-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: net: sched: Disallow replacing of child qdisc from one parent to another Lion Ackermann was able to create a UAF which can be abused for privilege escalation with the following script Step 1. create root qdisc tc qdisc add dev lo root handle 1:0 drr step2. a class for packet aggregation do demonstrate uaf tc class add dev lo classid 1:1 drr step3. a class for nesting tc class add dev lo classid 1:2 drr step4. a class to graft qdisc to tc class add dev lo classid 1:3 drr step5. tc qdisc add dev lo parent 1:1 handle 2:0 plug limit 1024 step6. tc qdisc add dev lo parent 1:2 handle 3:0 drr step7. tc class add dev lo classid 3:1 drr step 8. tc qdisc add dev lo parent 3:1 handle 4:0 pfifo step 9. Display the class/qdisc layout tc class ls dev lo class drr 1:1 root leaf 2: quantum 64Kb class drr 1:2 root leaf 3: quantum 64Kb class drr 3:1 root leaf 4: quantum 64Kb tc qdisc ls qdisc drr 1: dev lo root refcnt 2 qdisc plug 2: dev lo parent 1:1 qdisc pfifo 4: dev lo parent 3:1 limit 1000p qdisc drr 3: dev lo parent 1:2 step10. trigger the bug <=== prevented by this patch tc qdisc replace dev lo parent 1:3 handle 4:0 step 11. Redisplay again the qdiscs/classes tc class ls dev lo class drr 1:1 root leaf 2: quantum 64Kb class drr 1:2 root leaf 3: quantum 64Kb class drr 1:3 root leaf 4: quantum 64Kb class drr 3:1 root leaf 4: quantum 64Kb tc qdisc ls qdisc drr 1: dev lo root refcnt 2 qdisc plug 2: dev lo parent 1:1 qdisc pfifo 4: dev lo parent 3:1 refcnt 2 limit 1000p qdisc drr 3: dev lo parent 1:2 Observe that a) parent for 4:0 does not change despite the replace request. There can only be one parent. b) refcount has gone up by two for 4:0 and c) both class 1:3 and 3:1 are pointing to it. Step 12. send one packet to plug echo "" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10001)) step13. send one packet to the grafted fifo echo "" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10003)) step14. lets trigger the uaf tc class delete dev lo classid 1:3 tc class delete dev lo classid 1:1 The semantics of "replace" is for a del/add _on the same node_ and not a delete from one node(3:1) and add to another node (1:3) as in step10. While we could "fix" with a more complex approach there could be consequences to expectations so the patch takes the preventive approach of "disallow such config". Joint work with Lion Ackermann <nnamrec@gmail.com>

HighCVSS 7.8 · v3.1—No exploit Fix available

Published: Feb 13, 2025
Updated: Oct 15, 2026
EPSS: 0.2% · 14th percentile
CWE: CWE-416

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 31 / 40 · 7.8 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.2%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · Linux: 7.8; NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
linux	linux kernel	cpe:2.3:o:linux:linux_kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

linux linux kernel2.6.12 and later · before 5.4.291
linux linux kernel5.5 and later · before 5.10.235
linux linux kernel5.11 and later · before 5.15.179
linux linux kernel5.16 and later · before 6.1.129
linux linux kernel6.2 and later · before 6.6.76
linux linux kernel6.7 and later · before 6.12.13
linux linux kernel6.13 and later · before 6.13.2

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

Linux Linux
- 2.6.12affected
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before cd796e269123e1994bfc4e99dd76680ba0946a97affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before fe18c21d67dc7d1bcce1bba56515b1b0306db19baffected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 38646749d6e12f9d80a08d21ca39f0beca20230daffected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before deda09c0543a66fa51554abc5ffd723d99b191bfaffected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 7e2bd8c13b07e29a247c023c7444df23f9a79fd8affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 73c7e1d6898ccbeee126194dcc05f58b8a795e70affected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before 46c59ec33ec98aba20c15117630cae43a01404ccaffected · git
- 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and later · before bc50835e83f60f56e9bec2b392fb5544f250fb6faffected · git
- before 2.6.12not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	linux	before 6.1.129-1	6.1.129-1
Debian:13	linux	before 6.12.13-1	6.12.13-1
SUSE:Linux Enterprise Server 11 SP4 LTSS EXTREME CORE	kernel-default	before 3.0.101-108.183.1	3.0.101-108.183.1
SUSE:Linux Enterprise Server 11 SP4 LTSS EXTREME CORE	kernel-ec2	before 3.0.101-108.183.1	3.0.101-108.183.1
SUSE:Linux Enterprise Server 11 SP4 LTSS EXTREME CORE	kernel-source	before 3.0.101-108.183.1	3.0.101-108.183.1
SUSE:Linux Enterprise Server 11 SP4 LTSS EXTREME CORE	kernel-syms	before 3.0.101-108.183.1	3.0.101-108.183.1
SUSE:Linux Enterprise Server 11 SP4 LTSS EXTREME CORE	kernel-trace	before 3.0.101-108.183.1	3.0.101-108.183.1
SUSE:Linux Enterprise Server 11 SP4 LTSS EXTREME CORE	kernel-xen	before 3.0.101-108.183.1	3.0.101-108.183.1

Same product

linux: all records

Other highest-scoring records for the same primary product.

CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
90Now
CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
89Now
CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
85Now

Published before and after this one in the same product

← EarlierCVE-2025-21696Feb 12, 2025 · mm: clear uffd-wp PTE/PMD state on mremap()
22Monitor
← EarlierCVE-2025-21701Feb 13, 2025 · net: avoid race between device unregistration and ethnl ops
18Monitor
Later →CVE-2025-21702Feb 18, 2025 · pfifo_tail_enqueue: Drop new packet when sch->limit == 0
28Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
Linux Linux	38646749d6e12f9d80a08d21ca39f0beca20230d	Vendor (CNA)
Linux Linux	46c59ec33ec98aba20c15117630cae43a01404cc	Vendor (CNA)
Linux Linux	73c7e1d6898ccbeee126194dcc05f58b8a795e70	Vendor (CNA)
Linux Linux	7e2bd8c13b07e29a247c023c7444df23f9a79fd8	Vendor (CNA)
Linux Linux	bc50835e83f60f56e9bec2b392fb5544f250fb6f	Vendor (CNA)
Linux Linux	cd796e269123e1994bfc4e99dd76680ba0946a97	Vendor (CNA)
Linux Linux	deda09c0543a66fa51554abc5ffd723d99b191bf	Vendor (CNA)
Linux Linux	fe18c21d67dc7d1bcce1bba56515b1b0306db19b	Vendor (CNA)
cbl2 kernel 5.15.176.3-3 on CBL Mariner 2.0	5.15.180.1-1 · CBL-Mariner Releases	Microsoft (MSRC)
cbl2 kernel 5.15.176.3-3 on CBL-Mariner 2.0	5.15.180.1-1 · CBL-Mariner Releases	Microsoft (MSRC)
cbl2 kernel 5.15.180.1-1 on CBL Mariner 2.0	5.15.180.1-1 · CBL-Mariner Releases	Microsoft (MSRC)
debian:linux	6.1.129-1 · Debian:12	Package registry (OSV)
suse:kernel-default	3.0.101-108.183.1 · SUSE:Linux Enterprise Server 11 SP4 LTSS EXTREME CORE	Package registry (OSV)
suse:kernel-ec2	3.0.101-108.183.1 · SUSE:Linux Enterprise Server 11 SP4 LTSS EXTREME CORE	Package registry (OSV)
suse:kernel-source	3.0.101-108.183.1 · SUSE:Linux Enterprise Server 11 SP4 LTSS EXTREME CORE	Package registry (OSV)
suse:kernel-syms	3.0.101-108.183.1 · SUSE:Linux Enterprise Server 11 SP4 LTSS EXTREME CORE	Package registry (OSV)
suse:kernel-trace	3.0.101-108.183.1 · SUSE:Linux Enterprise Server 11 SP4 LTSS EXTREME CORE	Package registry (OSV)
suse:kernel-xen	3.0.101-108.183.1 · SUSE:Linux Enterprise Server 11 SP4 LTSS EXTREME CORE	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Someone with local access to the system can trigger it.
A low-privileged account is enough.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

Attack vector: Local
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

nvd-secondary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1free(dev->buf);
2/* ... another thread is still running ... */
3process(dev->buf);

Fixed

1lock(&dev->lock);
2free(dev->buf);
3dev->buf = NULL;
4unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

Fix✗ → ✓Sep 28, 2026, 10:11 PM UTC

For records you follow, these changes also arrive as notifications. →

References

git.kernel.org/stable/c/38646749d6e12f9d80a08d21ca39f0beca20230d

Show all references (10 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records