CVE-2025-38350

Published Jul 19, 2025

Last updated a month ago

CVSS high 7.8

Overview

Description
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.
Source
416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD status
Modified
Products
linux_kernel, debian_linux

Risk scores

CVSS 3.1

Type
Primary
Base score
7.8
Impact score
5.9
Exploitability score
1.8
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Severity
HIGH

Weaknesses

nvd@nist.gov
CWE-416

Social media

Hype score
Not currently trending

  1. 🚨 CRITICAL: Linux kernel vulnerability CVE-2025-38350 patched. Affects #Ubuntu GCP/Oracle cloud kernels. Allows remote system compromise. Read more: 👉 https://t.co/N5e4YR7Lxc #Security https://t.co/ScqkJwjsaG

    @Cezar_H_Linux

    19 Sept 2025

    40 Impressions

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  2. [ZDI-25-651|CVE-2025-38350] (Pwn2Own) Red Hat Enterprise Linux CBS Packet Scheduling Use-After-Free Local Privilege Escalation Vulnerability (CVSS 8.8; Credit: Gerrard Tai of STAR Labs SG Pte. Ltd.) https://t.co/4Fwz2yn3Hv

    @TheZDIBugs

    25 Jul 2025

    490 Impressions

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  3. Red Hat Enterprise Linux CBS Packet Scheduling Use-After-Free Local Privilege Escalation Vulnerability (CVE-2025-38350) #CVE202538350 #CyberSecurity #Linux #PrivilegeEscalationVulnerability #RedHat https://t.co/ADYycX5T4A https://t.co/pIhDWax17t

    @SystemTek_UK

    25 Jul 2025

    9 Impressions

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  4. CVE-2025-38350 In the Linux kernel, the following vulnerability has been resolved: net/sched: Always pass notifications when child class becomes empty Certain classful qdiscs may … https://t.co/Cg8pGBi9sv

    @CVEnew

    19 Jul 2025

    13 Impressions

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Configurations

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References

Sources include official advisories and independent security research.