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

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于存在内存释放后重用。

CVSS 7.8 · High EPSS 0.29% · P21

Affected Version Matrix 24

VendorProduct Version RangeStatus
Linux Linux 83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31< e395fec75ac2dbffc99b4bce57b7f1f3c5449f2c affected
216509dda290f6db92c816dd54b83c1df9da9e76< 7f31d74fcc556a9166b1bb20515542de7bb939d1 affected
c2047b0e216c8edce227d7c42f99ac2877dad0e4< 98a2c685293aae122f688cde11d9334dddc5d207 affected
10df49cfca73dfbbdb6c4150d859f7e8926ae427< 7b79ca9a1de6a428d486ff52fb3d602321c08f55 affected
3824c5fad18eeb7abe0c4fc966f29959552dca3e< 1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5 affected
356078a5c55ec8d2061fcc009fb8599f5b0527f9< 6312555249082d6d8cc5321ff725df05482d8b83 affected
f8d4bc455047cf3903cd6f85f49978987dbb3027< 839ecc583fa00fab785fde1c85a326743657fd32 affected
f8d4bc455047cf3903cd6f85f49978987dbb3027< 638ba5089324796c2ee49af10427459c2de35f71 affected
… +16 more rows
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I. Basic Information for CVE-2025-21703

Vulnerability Information
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Vulnerability Title
netem: Update sch->q.qlen before qdisc_tree_reduce_backlog()
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于存在内存释放后重用。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31 ~ e395fec75ac2dbffc99b4bce57b7f1f3c5449f2c -
Linux Linux 6.13 -

II. Public POCs for CVE-2025-21703

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III. Intelligence Information for CVE-2025-21703

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Patches & Fixes for CVE-2025-21703 (5)

Other References for CVE-2025-21703 (3)

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2025-21703

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