{"id":"CVE-2025-21703","state":"PUBLISHED","title":"netem: Update sch->q.qlen before qdisc_tree_reduce_backlog()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetem: Update sch->q.qlen before qdisc_tree_reduce_backlog()\n\nqdisc_tree_reduce_backlog() notifies parent qdisc only if child\nqdisc becomes empty, therefore we need to reduce the backlog of the\nchild qdisc before calling it. Otherwise it would miss the opportunity\nto call cops->qlen_notify(), in the case of DRR, it resulted in UAF\nsince DRR uses ->qlen_notify() to maintain its active list.","publishedAt":"2025-02-18T14:37:44.261Z","updatedAt":"2026-10-15T01:03:25.306Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31","status":"affected","lessThan":"e395fec75ac2dbffc99b4bce57b7f1f3c5449f2c","versionType":"git"},{"version":"216509dda290f6db92c816dd54b83c1df9da9e76","status":"affected","lessThan":"7f31d74fcc556a9166b1bb20515542de7bb939d1","versionType":"git"},{"version":"c2047b0e216c8edce227d7c42f99ac2877dad0e4","status":"affected","lessThan":"98a2c685293aae122f688cde11d9334dddc5d207","versionType":"git"},{"version":"10df49cfca73dfbbdb6c4150d859f7e8926ae427","status":"affected","lessThan":"7b79ca9a1de6a428d486ff52fb3d602321c08f55","versionType":"git"},{"version":"3824c5fad18eeb7abe0c4fc966f29959552dca3e","status":"affected","lessThan":"1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5","versionType":"git"},{"version":"356078a5c55ec8d2061fcc009fb8599f5b0527f9","status":"affected","lessThan":"6312555249082d6d8cc5321ff725df05482d8b83","versionType":"git"},{"version":"f8d4bc455047cf3903cd6f85f49978987dbb3027","status":"affected","lessThan":"839ecc583fa00fab785fde1c85a326743657fd32","versionType":"git"},{"version":"f8d4bc455047cf3903cd6f85f49978987dbb3027","status":"affected","lessThan":"638ba5089324796c2ee49af10427459c2de35f71","versionType":"git"},{"version":"5.4.288","status":"affected","lessThan":"5.4.291","versionType":"semver"},{"version":"5.10.232","status":"affected","lessThan":"5.10.235","versionType":"semver"},{"version":"5.15.175","status":"affected","lessThan":"5.15.179","versionType":"semver"},{"version":"6.1.121","status":"affected","lessThan":"6.1.129","versionType":"semver"},{"version":"6.6.67","status":"affected","lessThan":"6.6.78","versionType":"semver"},{"version":"6.12.6","status":"affected","lessThan":"6.12.14","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_netem.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.13","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.13","versionType":"semver"},{"version":"5.4.291","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.235","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.179","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.129","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.78","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.14","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.13.3","status":"unaffected","lessThanOrEqual":"6.13.*","versionType":"semver"},{"version":"6.14","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_netem.c"]}],"references":["https://git.kernel.org/stable/c/e395fec75ac2dbffc99b4bce57b7f1f3c5449f2c","https://git.kernel.org/stable/c/7f31d74fcc556a9166b1bb20515542de7bb939d1","https://git.kernel.org/stable/c/98a2c685293aae122f688cde11d9334dddc5d207","https://git.kernel.org/stable/c/7b79ca9a1de6a428d486ff52fb3d602321c08f55","https://git.kernel.org/stable/c/1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5","https://git.kernel.org/stable/c/6312555249082d6d8cc5321ff725df05482d8b83","https://git.kernel.org/stable/c/839ecc583fa00fab785fde1c85a326743657fd32","https://git.kernel.org/stable/c/638ba5089324796c2ee49af10427459c2de35f71","https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html","https://cert-portal.siemens.com/productcert/html/ssa-503939.html","https://cert-portal.siemens.com/productcert/html/ssa-784472.html"],"weaknesses":["CWE-416"],"ingestedAt":"2026-10-29T20:08:39.238Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2025/21xxx/CVE-2025-21703.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-21703","state":"PUBLISHED","datePublished":"2025-02-18T14:37:44.261Z","dateUpdated":"2026-10-15T01:03:25.306Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2024-12-29T08:45:45.751Z"},"containers":{"cna":{"title":"netem: Update sch->q.qlen before qdisc_tree_reduce_backlog()","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetem: Update sch->q.qlen before qdisc_tree_reduce_backlog()\n\nqdisc_tree_reduce_backlog() notifies parent qdisc only if child\nqdisc becomes empty, therefore we need to reduce the backlog of the\nchild qdisc before calling it. Otherwise it would miss the opportunity\nto call cops->qlen_notify(), in the case of DRR, it resulted in UAF\nsince DRR uses ->qlen_notify() to maintain its active list."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31","status":"affected","lessThan":"e395fec75ac2dbffc99b4bce57b7f1f3c5449f2c","versionType":"git"},{"version":"216509dda290f6db92c816dd54b83c1df9da9e76","status":"affected","lessThan":"7f31d74fcc556a9166b1bb20515542de7bb939d1","versionType":"git"},{"version":"c2047b0e216c8edce227d7c42f99ac2877dad0e4","status":"affected","lessThan":"98a2c685293aae122f688cde11d9334dddc5d207","versionType":"git"},{"version":"10df49cfca73dfbbdb6c4150d859f7e8926ae427","status":"affected","lessThan":"7b79ca9a1de6a428d486ff52fb3d602321c08f55","versionType":"git"},{"version":"3824c5fad18eeb7abe0c4fc966f29959552dca3e","status":"affected","lessThan":"1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5","versionType":"git"},{"version":"356078a5c55ec8d2061fcc009fb8599f5b0527f9","status":"affected","lessThan":"6312555249082d6d8cc5321ff725df05482d8b83","versionType":"git"},{"version":"f8d4bc455047cf3903cd6f85f49978987dbb3027","status":"affected","lessThan":"839ecc583fa00fab785fde1c85a326743657fd32","versionType":"git"},{"version":"f8d4bc455047cf3903cd6f85f49978987dbb3027","status":"affected","lessThan":"638ba5089324796c2ee49af10427459c2de35f71","versionType":"git"},{"version":"5.4.288","status":"affected","lessThan":"5.4.291","versionType":"semver"},{"version":"5.10.232","status":"affected","lessThan":"5.10.235","versionType":"semver"},{"version":"5.15.175","status":"affected","lessThan":"5.15.179","versionType":"semver"},{"version":"6.1.121","status":"affected","lessThan":"6.1.129","versionType":"semver"},{"version":"6.6.67","status":"affected","lessThan":"6.6.78","versionType":"semver"},{"version":"6.12.6","status":"affected","lessThan":"6.12.14","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_netem.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.13","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.13","versionType":"semver"},{"version":"5.4.291","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.235","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.179","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.129","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.78","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.14","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.13.3","status":"unaffected","lessThanOrEqual":"6.13.*","versionType":"semver"},{"version":"6.14","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_netem.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/e395fec75ac2dbffc99b4bce57b7f1f3c5449f2c"},{"url":"https://git.kernel.org/stable/c/7f31d74fcc556a9166b1bb20515542de7bb939d1"},{"url":"https://git.kernel.org/stable/c/98a2c685293aae122f688cde11d9334dddc5d207"},{"url":"https://git.kernel.org/stable/c/7b79ca9a1de6a428d486ff52fb3d602321c08f55"},{"url":"https://git.kernel.org/stable/c/1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5"},{"url":"https://git.kernel.org/stable/c/6312555249082d6d8cc5321ff725df05482d8b83"},{"url":"https://git.kernel.org/stable/c/839ecc583fa00fab785fde1c85a326743657fd32"},{"url":"https://git.kernel.org/stable/c/638ba5089324796c2ee49af10427459c2de35f71"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"UAF in netem/DRR qdisc interaction. qdisc_tree_reduce_backlog() called before qlen update misses DRR qlen_notify, leaving freed class on active list. 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