Linux Kernel up to 6.16-rc4 sched qlen_notify use after free

CVSS Meta Temp Score
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CTI Interest Score
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7.7$0-$5k0.00

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.16-rc4. It has been rated as critical. This affects the function qlen_notify of the component sched. Performing a manipulation results in use after free. This vulnerability is known as CVE-2025-38350. No exploit is available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.16-rc4. It has been classified as critical. This affects the function qlen_notify of the component sched. The manipulation with an unknown input leads to a use after free vulnerability. CWE is classifying the issue as CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: net/sched: Always pass notifications when child class becomes empty Certain classful qdiscs may invoke their classes' dequeue handler on an enqueue operation. This may unexpectedly empty the child qdisc and thus make an in-flight class passive via qlen_notify(). Most qdiscs do not expect such behaviour at this point in time and may re-activate the class eventually anyways which will lead to a use-after-free. The referenced fix commit attempted to fix this behavior for the HFSC case by moving the backlog accounting around, though this turned out to be incomplete since the parent's parent may run into the issue too. The following reproducer demonstrates this use-after-free: tc qdisc add dev lo root handle 1: drr tc filter add dev lo parent 1: basic classid 1:1 tc class add dev lo parent 1: classid 1:1 drr tc qdisc add dev lo parent 1:1 handle 2: hfsc def 1 tc class add dev lo parent 2: classid 2:1 hfsc rt m1 8 d 1 m2 0 tc qdisc add dev lo parent 2:1 handle 3: netem tc qdisc add dev lo parent 3:1 handle 4: blackhole echo 1 | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888 tc class delete dev lo classid 1:1 echo 1 | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888 Since backlog accounting issues leading to a use-after-frees on stale class pointers is a recurring pattern at this point, this patch takes a different approach. Instead of trying to fix the accounting, the patch ensures that qdisc_tree_reduce_backlog always calls qlen_notify when the child qdisc is empty. This solves the problem because deletion of qdiscs always involves a call to qdisc_reset() and / or qdisc_purge_queue() which ultimately resets its qlen to 0 thus causing the following qdisc_tree_reduce_backlog() to report to the parent. Note that this may call qlen_notify on passive classes multiple times. This is not a problem after the recent patch series that made all the classful qdiscs qlen_notify() handlers idempotent.

It is possible to read the advisory at git.kernel.org. This vulnerability is uniquely identified as CVE-2025-38350 since 04/16/2025. The exploitability is told to be easy. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 02/20/2026).

The vulnerability scanner Nessus provides a plugin with the ID 249324 (Oracle Linux 9 : kernel (ELSA-2025-13602)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 5.4.296, 5.10.240, 5.15.187, 6.1.144, 6.6.97, 6.12.37, 6.15.6 or 6.16-rc5 eliminates this vulnerability. Applying the patch 3b290923ad2b23596208c1e29520badef4356a43/e9921b57dca05ac5f4fa1fa8e993d4f0ee52e2b7/e269f29e9395527bc00c213c6b15da04ebb35070/7874c9c132e906a52a187d045995b115973c93fb/f680a4643c6f71e758d8fe0431a958e9a6a4f59d/a553afd91f55ff39b1e8a1c4989a29394c9e0472/a44acdd9e84a211989ff4b9b92bf3545d8456ad5/103406b38c600fec1fe375a77b27d87e314aea09 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (249324), EUVD (EUVD-2025-21953) and CERT Bund (WID-SEC-2025-1613). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

  • Google Container-Optimized OS
  • Debian Linux
  • Red Hat Enterprise Linux
  • Ubuntu Linux
  • SUSE Linux
  • Oracle Linux
  • SUSE openSUSE
  • RESF Rocky Linux
  • Dell Avamar
  • IBM TXSeries
  • Open Source Linux Kernel
  • Dell NetWorker
  • Dell Secure Connect Gateway
  • IBM QRadar SIEM

Productinfo

Type

Vendor

Name

Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 7.9
VulDB Meta Temp Score: 7.7

VulDB Base Score: 8.0
VulDB Temp Score: 7.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 7.8
NVD Vector: 🔒

CVSSv2info

AVACAuCIA
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💳💳💳💳💳💳
💳💳💳💳💳💳
VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Use after free
CWE: CWE-416 / CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 249324
Nessus Name: Oracle Linux 9 : kernel (ELSA-2025-13602)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 5.4.296/5.10.240/5.15.187/6.1.144/6.6.97/6.12.37/6.15.6/6.16-rc5
Patch: 3b290923ad2b23596208c1e29520badef4356a43/e9921b57dca05ac5f4fa1fa8e993d4f0ee52e2b7/e269f29e9395527bc00c213c6b15da04ebb35070/7874c9c132e906a52a187d045995b115973c93fb/f680a4643c6f71e758d8fe0431a958e9a6a4f59d/a553afd91f55ff39b1e8a1c4989a29394c9e0472/a44acdd9e84a211989ff4b9b92bf3545d8456ad5/103406b38c600fec1fe375a77b27d87e314aea09

Timelineinfo

04/16/2025 CVE reserved
07/19/2025 +94 days Advisory disclosed
07/19/2025 +0 days VulDB entry created
02/20/2026 +216 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-38350 (🔒)
GCVE (CVE): GCVE-0-2025-38350
GCVE (VulDB): GCVE-100-316995
EUVD: 🔒
CERT Bund: WID-SEC-2025-1613 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 07/19/2025 09:24
Updated: 02/20/2026 11:01
Changes: 07/19/2025 09:24 (59), 07/19/2025 11:24 (1), 07/21/2025 14:32 (7), 08/12/2025 12:41 (1), 08/15/2025 04:05 (2), 09/01/2025 10:08 (1), 10/09/2025 14:23 (1), 11/02/2025 15:36 (1), 12/16/2025 22:50 (12), 02/20/2026 11:01 (1)
Complete: 🔍
Cache ID: 216::103

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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