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NVD / CVE Program· CNA Linux

CVE-2025-21703: netem: Update sch->q.qlen before qdisc_tree_reduce_backlog()

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: 0.30% (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 1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5, 5.10.235, 5.15.179; 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 1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5, 5.10.235, 5.15.179; 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: netem: Update sch->q.qlen before qdisc_tree_reduce_backlog() qdisc_tree_reduce_backlog() notifies parent qdisc only if child qdisc becomes empty, therefore we need to reduce the backlog of the child qdisc before calling it. Otherwise it would miss the opportunity to call cops->qlen_notify(), in the case of DRR, it resulted in UAF since DRR uses ->qlen_notify() to maintain its active list.

HighCVSS 7.8 · v3.1—No exploit Fix available
Published
Feb 18, 2025
Updated
Oct 15, 2026
EPSS
0.3% · 22th percentile

Report tools

JSON

Action score

31

Monitor

Low priority for now.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

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

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2025-21703

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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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.

VendorProduct
linuxlinux kernel

Affected versions

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

  • linux linux kernel5.4.288 and later · before 5.4.291
  • linux linux kernel5.10.232 and later · before 5.10.235
  • linux linux kernel5.15.175 and later · before 5.15.179
  • linux linux kernel6.1.121 and later · before 6.1.129
  • linux linux kernel6.6.67 and later · before 6.6.78
  • linux linux kernel6.12.6 and later · before 6.12.14
  • linux linux kernel6.13 and later · before 6.13.3
  • linux linux kernel6.14

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

    • 6.13affected
    • 83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31 and later · before e395fec75ac2dbffc99b4bce57b7f1f3c5449f2caffected · git
    • 216509dda290f6db92c816dd54b83c1df9da9e76 and later · before 7f31d74fcc556a9166b1bb20515542de7bb939d1affected · git
    • c2047b0e216c8edce227d7c42f99ac2877dad0e4 and later · before 98a2c685293aae122f688cde11d9334dddc5d207affected · git
    • 10df49cfca73dfbbdb6c4150d859f7e8926ae427 and later · before 7b79ca9a1de6a428d486ff52fb3d602321c08f55affected · git
    • 3824c5fad18eeb7abe0c4fc966f29959552dca3e and later · before 1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5affected · git
    • 356078a5c55ec8d2061fcc009fb8599f5b0527f9 and later · before 6312555249082d6d8cc5321ff725df05482d8b83affected · git
    • f8d4bc455047cf3903cd6f85f49978987dbb3027 and later · before 839ecc583fa00fab785fde1c85a326743657fd32affected · git
    • f8d4bc455047cf3903cd6f85f49978987dbb3027 and later · before 638ba5089324796c2ee49af10427459c2de35f71affected · git
    • 5.4.288 and later · before 5.4.291affected · semver

Package-level exposure

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

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 6.1.129-16.1.129-1
Debian:13linuxbefore 6.12.15-16.12.15-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • 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
  • CVE-2016-5195Race condition in mm/gup.c in the Linux kernel 2.x through 4.x before 4.8.3 allows local users to gain privileges by leveraging incorrect haKEV
    83Now

Published before and after this one in the same product

  • ← EarlierCVE-2025-21700Feb 13, 2025 · net: sched: Disallow replacing of child qdisc from one parent to another
    31Monitor
  • ← EarlierCVE-2025-21702Feb 18, 2025 · pfifo_tail_enqueue: Drop new packet when sch->limit == 0
    28Monitor
  • Later →CVE-2025-21704Feb 22, 2025 · usb: cdc-acm: Check control transfer buffer size before access
    31Monitor

Remediation

Which version to upgrade to

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

Product / packageFixed versionSource
Linux Linux1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5Vendor (CNA)
Linux Linux5.10.235Vendor (CNA)
Linux Linux5.15.179Vendor (CNA)
Linux Linux5.4.291Vendor (CNA)
Linux Linux6.1.129Vendor (CNA)
Linux Linux6.12.14Vendor (CNA)
Linux Linux6.6.78Vendor (CNA)
Linux Linux6312555249082d6d8cc5321ff725df05482d8b83Vendor (CNA)
Linux Linux638ba5089324796c2ee49af10427459c2de35f71Vendor (CNA)
Linux Linux7b79ca9a1de6a428d486ff52fb3d602321c08f55Vendor (CNA)
Linux Linux7f31d74fcc556a9166b1bb20515542de7bb939d1Vendor (CNA)
Linux Linux839ecc583fa00fab785fde1c85a326743657fd32Vendor (CNA)
Linux Linux98a2c685293aae122f688cde11d9334dddc5d207Vendor (CNA)
Linux Linuxe395fec75ac2dbffc99b4bce57b7f1f3c5449f2cVendor (CNA)
cbl2 kernel 5.15.176.3-3 on CBL Mariner 2.05.15.180.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
cbl2 kernel 5.15.176.3-3 on CBL-Mariner 2.05.15.180.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
cbl2 kernel 5.15.180.1-1 on CBL Mariner 2.05.15.180.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
debian:linux6.1.129-1 · Debian:12Package 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.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

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

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

Fixed

c
lock(&dev->lock);free(dev->buf);dev->buf = NULL;unlock(&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

  1. Fix✗ → ✓

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

References

Show all references (10 more)

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

All records