CVE-2025-21702

{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2025-21702", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2024-12-29T08:45:45.748Z", "datePublished": "2025-02-18T14:37:43.429Z", "dateUpdated": "2026-11-10T12:34:40.216Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T11:53:45.209Z"}, "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\npfifo_tail_enqueue: Drop new packet when sch->limit == 0\n\nExpected behaviour:\nIn case we reach scheduler's limit, pfifo_tail_enqueue() will drop a\npacket in scheduler's queue and decrease scheduler's qlen by one.\nThen, pfifo_tail_enqueue() enqueue new packet and increase\nscheduler's qlen by one. Finally, pfifo_tail_enqueue() return\n`NET_XMIT_CN` status code.\n\nWeird behaviour:\nIn case we set `sch->limit == 0` and trigger pfifo_tail_enqueue() on a\nscheduler that has no packet, the 'drop a packet' step will do nothing.\nThis means the scheduler's qlen still has value equal 0.\nThen, we continue to enqueue new packet and increase scheduler's qlen by\none. In summary, we can leverage pfifo_tail_enqueue() to increase qlen by\none and return `NET_XMIT_CN` status code.\n\nThe problem is:\nLet's say we have two qdiscs: Qdisc_A and Qdisc_B.\n - Qdisc_A's type must have '->graft()' function to create parent/child relationship.\n Let's say Qdisc_A's type is `hfsc`. Enqueue packet to this qdisc will trigger `hfsc_enqueue`.\n - Qdisc_B's type is pfifo_head_drop. Enqueue packet to this qdisc will trigger `pfifo_tail_enqueue`.\n - Qdisc_B is configured to have `sch->limit == 0`.\n - Qdisc_A is configured to route the enqueued's packet to Qdisc_B.\n\nEnqueue packet through Qdisc_A will lead to:\n - hfsc_enqueue(Qdisc_A) -> pfifo_tail_enqueue(Qdisc_B)\n - Qdisc_B->q.qlen += 1\n - pfifo_tail_enqueue() return `NET_XMIT_CN`\n - hfsc_enqueue() check for `NET_XMIT_SUCCESS` and see `NET_XMIT_CN` => hfsc_enqueue() don't increase qlen of Qdisc_A.\n\nThe whole process lead to a situation where Qdisc_A->q.qlen == 0 and Qdisc_B->q.qlen == 1.\nReplace 'hfsc' with other type (for example: 'drr') still lead to the same problem.\nThis violate the design where parent's qlen should equal to the sum of its childrens'qlen.\n\nBug impact: This issue can be used for user->kernel privilege escalation when it is reachable."}], "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": "Deterministic qlen underflow via pfifo_tail_enqueue with limit=0. Enables user-to-kernel privilege escalation through qlen accounting inconsistency in parent-child qdisc relationship."}]}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["net/sched/sch_fifo.c"], "versions": [{"version": "57dbb2d83d100ea601c54fe129bfde0678db5dee", "lessThan": "78285b53266d6d51fa4ff504a23df03852eba84e", "status": "affected", "versionType": "git"}, {"version": "57dbb2d83d100ea601c54fe129bfde0678db5dee", "lessThan": "7a9723ec27aff5674f1fd4934608937f1d650980", "status": "affected", "versionType": "git"}, {"version": "57dbb2d83d100ea601c54fe129bfde0678db5dee", "lessThan": "a56a6e8589a9b98d8171611fbcc1e45a15fd2455", "status": "affected", "versionType": "git"}, {"version": "57dbb2d83d100ea601c54fe129bfde0678db5dee", "lessThan": "020ecb76812a0526f4130ab5aeb6dc7c773e7ab9", "status": "affected", "versionType": "git"}, {"version": "57dbb2d83d100ea601c54fe129bfde0678db5dee", "lessThan": "79a955ea4a2e5ddf4a36328959de0de496419888", "status": "affected", "versionType": "git"}, {"version": "57dbb2d83d100ea601c54fe129bfde0678db5dee", "lessThan": "e40cb34b7f247fe2e366fd192700d1b4f38196ca", "status": "affected", "versionType": "git"}, {"version": "57dbb2d83d100ea601c54fe129bfde0678db5dee", "lessThan": "b6a079c3b6f95378f26e2aeda520cb3176f7067b", "status": "affected", "versionType": "git"}, {"version": "57dbb2d83d100ea601c54fe129bfde0678db5dee", "lessThan": "647cef20e649c576dff271e018d5d15d998b629d", "status": "affected", "versionType": "git"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["net/sched/sch_fifo.c"], "versions": [{"version": "2.6.34", "status": "affected"}, {"version": "0", "lessThan": "2.6.34", "status": "unaffected", "versionType": "semver"}, {"version": "5.4.291", "lessThanOrEqual": "5.4.*", "status": "unaffected", "versionType": "semver"}, {"version": "5.10.235", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver"}, {"version": "5.15.179", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.1.130", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.6.83", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.12.14", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.13.3", "lessThanOrEqual": "6.13.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.14", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix"}]}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "5.4.291"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "5.10.235"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "5.15.179"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "6.1.130"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "6.6.83"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "6.12.14"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.34", "versionEndExcluding": "6.13.3"}, {"vulnerable": true, "criteria": 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"https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html"}, {"url": "https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html"}], "providerMetadata": {"orgId": "af854a3a-2127-422b-91ae-364da2661108", "shortName": "CVE", "dateUpdated": "2025-11-03T19:35:50.649Z"}}, {"x_adpType": "supplier", "providerMetadata": {"orgId": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e", "shortName": "siemens-SADP", "dateUpdated": "2026-11-10T12:34:40.216Z"}, "affected": [{"vendor": "Siemens", "product": "SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)", "versions": [{"status": "affected", "version": "V3.1.5", "lessThan": "*", "versionType": "custom"}], "defaultStatus": "unknown"}, {"vendor": "Siemens", "product": "SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)", "versions": [{"status": "affected", "version": "V3.1.6", "lessThan": "*", "versionType": "custom"}], "defaultStatus": "unknown"}, {"vendor": "Siemens", "product": "SIMATIC S7-1500 CPU 1518-4 PN/DP MFP 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{}

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"5.11", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "26997835-273D-4841-ABD3-4696059AC299", "versionEndExcluding": "6.1.130", "versionStartIncluding": "5.16", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "7D9F642F-6E05-4926-B0FE-62F95B7266BC", "versionEndExcluding": "6.6.83", "versionStartIncluding": "6.2", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "033BB7EE-C9A2-45EA-BAC9-87BB9D951BCD", "versionEndExcluding": "6.12.14", "versionStartIncluding": "6.7", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "0E92CEE3-1FC3-4AFC-A513-DEDBA7414F00", "versionEndExcluding": "6.13.3", "versionStartIncluding": "6.13", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:6.14:rc1:*:*:*:*:*:*", "matchCriteriaId": "186716B6-2B66-4BD0-852E-D48E71C0C85F", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\npfifo_tail_enqueue: Drop new packet when sch->limit == 0\n\nExpected behaviour:\nIn case we reach scheduler's limit, pfifo_tail_enqueue() will drop a\npacket in scheduler's queue and decrease scheduler's qlen by one.\nThen, pfifo_tail_enqueue() enqueue new packet and increase\nscheduler's qlen by one. Finally, pfifo_tail_enqueue() return\n`NET_XMIT_CN` status code.\n\nWeird behaviour:\nIn case we set `sch->limit == 0` and trigger pfifo_tail_enqueue() on a\nscheduler that has no packet, the 'drop a packet' step will do nothing.\nThis means the scheduler's qlen still has value equal 0.\nThen, we continue to enqueue new packet and increase scheduler's qlen by\none. In summary, we can leverage pfifo_tail_enqueue() to increase qlen by\none and return `NET_XMIT_CN` status code.\n\nThe problem is:\nLet's say we have two qdiscs: Qdisc_A and Qdisc_B.\n - Qdisc_A's type must have '->graft()' function to create parent/child relationship.\n Let's say Qdisc_A's type is `hfsc`. Enqueue packet to this qdisc will trigger `hfsc_enqueue`.\n - Qdisc_B's type is pfifo_head_drop. Enqueue packet to this qdisc will trigger `pfifo_tail_enqueue`.\n - Qdisc_B is configured to have `sch->limit == 0`.\n - Qdisc_A is configured to route the enqueued's packet to Qdisc_B.\n\nEnqueue packet through Qdisc_A will lead to:\n - hfsc_enqueue(Qdisc_A) -> pfifo_tail_enqueue(Qdisc_B)\n - Qdisc_B->q.qlen += 1\n - pfifo_tail_enqueue() return `NET_XMIT_CN`\n - hfsc_enqueue() check for `NET_XMIT_SUCCESS` and see `NET_XMIT_CN` => hfsc_enqueue() don't increase qlen of Qdisc_A.\n\nThe whole process lead to a situation where Qdisc_A->q.qlen == 0 and Qdisc_B->q.qlen == 1.\nReplace 'hfsc' with other type (for example: 'drr') still lead to the same problem.\nThis violate the design where parent's qlen should equal to the sum of its childrens'qlen.\n\nBug impact: This issue can be used for user->kernel privilege escalation when it is reachable."}, {"lang": "es", "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: pfifo_tail_enqueue: Descartar nuevo paquete cuando sch->limit == 0 Comportamiento esperado: En caso de que alcancemos el l\u00edmite del planificador, pfifo_tail_enqueue() descartar\u00e1 un paquete en la cola del planificador y disminuir\u00e1 el qlen del planificador en uno. Luego, pfifo_tail_enqueue() pone en cola un nuevo paquete y aumenta el qlen del planificador en uno. Finalmente, pfifo_tail_enqueue() devuelve el c\u00f3digo de estado `NET_XMIT_CN`. Comportamiento extra\u00f1o: En caso de que establezcamos `sch->limit == 0` y activemos pfifo_tail_enqueue() en un planificador que no tiene ning\u00fan paquete, el paso 'descartar un paquete' no har\u00e1 nada. Esto significa que el qlen del planificador todav\u00eda tiene un valor igual a 0. Luego, continuamos poniendo en cola un nuevo paquete y aumentamos el qlen del planificador en uno. En resumen, podemos aprovechar pfifo_tail_enqueue() para aumentar qlen en uno y devolver el c\u00f3digo de estado `NET_XMIT_CN`. El problema es: digamos que tenemos dos qdiscs: Qdisc_A y Qdisc_B. - El tipo de Qdisc_A debe tener la funci\u00f3n '->graft()' para crear una relaci\u00f3n padre/hijo. Digamos que el tipo de Qdisc_A es `hfsc`. Poner en cola un paquete en esta qdisc activar\u00e1 `hfsc_enqueue`. - El tipo de Qdisc_B es pfifo_head_drop. Poner en cola un paquete en esta qdisc activar\u00e1 `pfifo_tail_enqueue`. - Qdisc_B est\u00e1 configurado para tener `sch->limit == 0`. - Qdisc_A est\u00e1 configurado para enrutar el paquete en cola a Qdisc_B. Poner en cola un paquete a trav\u00e9s de Qdisc_A conducir\u00e1 a: - hfsc_enqueue(Qdisc_A) -> pfifo_tail_enqueue(Qdisc_B) - Qdisc_B->q.qlen += 1 - pfifo_tail_enqueue() devuelve `NET_XMIT_CN` - hfsc_enqueue() comprueba `NET_XMIT_SUCCESS` y ve `NET_XMIT_CN` => hfsc_enqueue() no aumenta el qlen de Qdisc_A. Todo el proceso conduce a una situaci\u00f3n en la que Qdisc_A->q.qlen == 0 y Qdisc_B->q.qlen == 1. Reemplazar 'hfsc' por otro tipo (por ejemplo: 'drr') sigue conduciendo al mismo problema. Esto viola el dise\u00f1o donde el qlen del padre debe ser igual a la suma del qlen de sus hijos. Impacto del error: este problema se puede utilizar para la escalada de privilegios de usuario a kernel cuando sea posible."}], "id": "CVE-2025-21702", "lastModified": "2026-11-10T13:17:32.973", "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": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary"}, {"cvssData": {"attackComplexity": "HIGH", "attackVector": "LOCAL", "availabilityImpact": "HIGH", "baseScore": 7.0, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 1.0, "impactScore": 5.9, "source": "nvd@nist.gov", "type": "Primary"}]}, "published": "2025-02-18T15:15:18.530", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/020ecb76812a0526f4130ab5aeb6dc7c773e7ab9"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/647cef20e649c576dff271e018d5d15d998b629d"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/78285b53266d6d51fa4ff504a23df03852eba84e"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/79a955ea4a2e5ddf4a36328959de0de496419888"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/7a9723ec27aff5674f1fd4934608937f1d650980"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/a56a6e8589a9b98d8171611fbcc1e45a15fd2455"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/b6a079c3b6f95378f26e2aeda520cb3176f7067b"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/e40cb34b7f247fe2e366fd192700d1b4f38196ca"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "url": "https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "url": "https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html"}, {"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e", "url": "https://cert-portal.siemens.com/productcert/html/ssa-019113.html"}, {"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e", "url": "https://cert-portal.siemens.com/productcert/html/ssa-082556.html"}, {"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e", "url": "https://cert-portal.siemens.com/productcert/html/ssa-457936.html"}, {"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e", "url": "https://cert-portal.siemens.com/productcert/html/ssa-784472.html"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Modified", "weaknesses": [{"description": [{"lang": "en", "value": "NVD-CWE-noinfo"}], "source": "nvd@nist.gov", "type": "Primary"}]}

{"bugzilla": {"description": "kernel: pfifo_tail_enqueue: Drop new packet when sch->limit == 0", "id": "2346272", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2346272"}, "csaw": false, "cvss3": {"cvss3_base_score": "7.0", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H", "status": "draft"}, "cwe": "CWE-438", "details": ["In the Linux kernel, the following vulnerability has been resolved:\npfifo_tail_enqueue: Drop new packet when sch->limit == 0\nExpected behaviour:\nIn case we reach scheduler's limit, pfifo_tail_enqueue() will drop a\npacket in scheduler's queue and decrease scheduler's qlen by one.\nThen, pfifo_tail_enqueue() enqueue new packet and increase\nscheduler's qlen by one. Finally, pfifo_tail_enqueue() return\n`NET_XMIT_CN` status code.\nWeird behaviour:\nIn case we set `sch->limit == 0` and trigger pfifo_tail_enqueue() on a\nscheduler that has no packet, the 'drop a packet' step will do nothing.\nThis means the scheduler's qlen still has value equal 0.\nThen, we continue to enqueue new packet and increase scheduler's qlen by\none. In summary, we can leverage pfifo_tail_enqueue() to increase qlen by\none and return `NET_XMIT_CN` status code.\nThe problem is:\nLet's say we have two qdiscs: Qdisc_A and Qdisc_B.\n- Qdisc_A's type must have '->graft()' function to create parent/child relationship.\nLet's say Qdisc_A's type is `hfsc`. Enqueue packet to this qdisc will trigger `hfsc_enqueue`.\n- Qdisc_B's type is pfifo_head_drop. Enqueue packet to this qdisc will trigger `pfifo_tail_enqueue`.\n- Qdisc_B is configured to have `sch->limit == 0`.\n- Qdisc_A is configured to route the enqueued's packet to Qdisc_B.\nEnqueue packet through Qdisc_A will lead to:\n- hfsc_enqueue(Qdisc_A) -> pfifo_tail_enqueue(Qdisc_B)\n- Qdisc_B->q.qlen += 1\n- pfifo_tail_enqueue() return `NET_XMIT_CN`\n- hfsc_enqueue() check for `NET_XMIT_SUCCESS` and see `NET_XMIT_CN` => hfsc_enqueue() don't increase qlen of Qdisc_A.\nThe whole process lead to a situation where Qdisc_A->q.qlen == 0 and Qdisc_B->q.qlen == 1.\nReplace 'hfsc' with other type (for example: 'drr') still lead to the same problem.\nThis violate the design where parent's qlen should equal to the sum of its childrens'qlen.\nBug impact: This issue can be used for user->kernel privilege escalation when it is reachable."], "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-2025-21702", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Out of support scope", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Out of support scope", "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": "Affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2025-02-18T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2025-21702\nhttps://nvd.nist.gov/vuln/detail/CVE-2025-21702\nhttps://lore.kernel.org/linux-cve-announce/2025021847-CVE-2025-21702-3aa3@gregkh/T"], "statement": "The default scheduler is pfifo_fast (and fd_codel for rhel8). This bug in BFIFO (sch_fifo) scheduler is not easy triggerable (requires usage of two qdiscs with special configuration). Both cannot trigger it before sch_fifo enabled. Rated to be Moderate.", "threat_severity": "Moderate"}

{"analysis": {"en": {"generated_at": "2026-04-29T01:02:22.994409+00:00", "value": {"mitigation_remediation": ["Apply the latest Linux kernel update that fixes the pfifo_head_drop enqueue implementation.", "Avoid creating child pfifo_head_drop qdiscs with a limit of zero; use a positive limit or a different qdisc type such as pfifo_fast or none.", "If a kernel update is not immediately possible, remove the vulnerable qdisc entirely or replace it with a stable scheduler to eliminate the code path.", "Restrict non\u2011privileged users from executing traffic\u2011control commands using SELinux, AppArmor, or similar access controls to reduce the attack surface."], "summary": {"action": "Immediate Patch", "impact": "Privilege Escalation"}, "threat_synthesis": {"affected_systems": "Linux kernel versions that include the pfifo_head_drop queue and in which this code path exists are affected. The CVE references a known bug in kernel 6.14 release candidate 1, indicating that kernels around that version, and likely earlier ones containing the same implementation, are vulnerable. The issue manifests when a parent scheduler enqueues a packet to a child pfifo_head_drop qdisc configured with a limit of zero, a scenario that can occur in standard Linux distributions that provide the tc command interface.", "description_and_impact": "The flawed pfifo_head_drop enqueue logic increments the child queue length without correctly updating the parent, breaking the invariant that a parent qdisc\u2019s length equals the sum of its children\u2019s lengths. This logic error, classified as CWE\u2011438, can corrupt kernel state during packet scheduling and, as the CVE notes, lead to privilege escalation when the defect is reachable.", "risk_and_exploitability": "The CVSS score of 7.8 signals high severity. The EPSS score of less than 1% suggests that exploitation is presently rare, and the vulnerability is not listed in CISA KEV, though that does not lessen potential risk. The likely attack vector is local manipulation of traffic\u2011control settings, which requires user\u2011level access to execute tc commands. Successful exploitation could corrupt kernel data structures and enable a local attacker to gain elevated privileges, making the impact system\u2011wide if the buggy code path is triggered."}}}}, "created": "2026-04-29T01:15:44.722082+00:00", "updated": "2026-04-29T01:15:44.722094+00:00", "vendors": []}