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

Type: advisorySource: Official CVE List1 source record

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.

Announced Group revision 1
Original source ↗

CVE-2025-21703

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2025-21703

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31",
        "lessThan": "e395fec75ac2dbffc99b4bce57b7f1f3c5449f2c",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "216509dda290f6db92c816dd54b83c1df9da9e76",
        "lessThan": "7f31d74fcc556a9166b1bb20515542de7bb939d1",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "c2047b0e216c8edce227d7c42f99ac2877dad0e4",
        "lessThan": "98a2c685293aae122f688cde11d9334dddc5d207",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "10df49cfca73dfbbdb6c4150d859f7e8926ae427",
        "lessThan": "7b79ca9a1de6a428d486ff52fb3d602321c08f55",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "3824c5fad18eeb7abe0c4fc966f29959552dca3e",
        "lessThan": "1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "356078a5c55ec8d2061fcc009fb8599f5b0527f9",
        "lessThan": "6312555249082d6d8cc5321ff725df05482d8b83",
        "versionType": "git"
      },
      {
        "status": "affected",
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        "lessThan": "839ecc583fa00fab785fde1c85a326743657fd32",
        "versionType": "git"
      },
      {
        "status": "affected",
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        "lessThan": "638ba5089324796c2ee49af10427459c2de35f71",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "5.4.288",
        "lessThan": "5.4.291",
        "versionType": "semver"
      },
      {
        "status": "affected",
        "version": "5.10.232",
        "lessThan": "5.10.235",
        "versionType": "semver"
      },
      {
        "status": "affected",
        "version": "5.15.175",
        "lessThan": "5.15.179",
        "versionType": "semver"
      },
      {
        "status": "affected",
        "version": "6.1.121",
        "lessThan": "6.1.129",
        "versionType": "semver"
      },
      {
        "status": "affected",
        "version": "6.6.67",
        "lessThan": "6.6.78",
        "versionType": "semver"
      },
      {
        "status": "affected",
        "version": "6.12.6",
        "lessThan": "6.12.14",
        "versionType": "semver"
      }
    ],
    "programFiles": [
      "net/sched/sch_netem.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "6.13"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "6.13",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "5.4.291",
        "versionType": "semver",
        "lessThanOrEqual": "5.4.*"
      },
      {
        "status": "unaffected",
        "version": "5.10.235",
        "versionType": "semver",
        "lessThanOrEqual": "5.10.*"
      },
      {
        "status": "unaffected",
        "version": "5.15.179",
        "versionType": "semver",
        "lessThanOrEqual": "5.15.*"
      },
      {
        "status": "unaffected",
        "version": "6.1.129",
        "versionType": "semver",
        "lessThanOrEqual": "6.1.*"
      },
      {
        "status": "unaffected",
        "version": "6.6.78",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.14",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.13.3",
        "versionType": "semver",
        "lessThanOrEqual": "6.13.*"
      },
      {
        "status": "unaffected",
        "version": "6.14",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "net/sched/sch_netem.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2025-21703

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#26910 · Revision 1
Added to Heist Feed
Publisher date
Read the original announcement

Revision history

  1. CVE-2025-21703 · Revision 1Source updated