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The issue occurs due to a time-of-check/time-of-use condition\nin hfsc_change_class() when working with certain child qdiscs like netem\nor codel.\n\nThe vulnerability works as follows:\n1. hfsc_change_class() checks if a class has packets (q.qlen != 0)\n2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g.,\n codel, netem) might drop packets and empty the queue\n3. The code continues assuming the queue is still non-empty, adding\n the class to vttree\n4. This breaks HFSC scheduler assumptions that only non-empty classes\n are in vttree\n5. Later, when the class is destroyed, this can lead to a Use-After-Free\n\nThe fix adds a second queue length check after qdisc_peek_len() to verify\nthe queue wasn't emptied."}, {"lang": "es", "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: net_sched: hfsc: Se corrige una vulnerabilidad de UAF en la gesti\u00f3n de clases. Este parche corrige una vulnerabilidad de use-after-free en la gesti\u00f3n de clases de qdisc HFSC. El problema se produce debido a una condici\u00f3n de tiempo de comprobaci\u00f3n/tiempo de uso en hfsc_change_class() al trabajar con ciertas qdiscs secundarias como netem o codel. La vulnerabilidad funciona de la siguiente manera: 1. hfsc_change_class() verifica si una clase tiene paquetes (q.qlen != 0) 2. Luego llama a qdisc_peek_len(), que para ciertos qdiscs (por ejemplo, codel, netem) puede descartar paquetes y vaciar la cola 3. El c\u00f3digo contin\u00faa asumiendo que la cola todav\u00eda no est\u00e1 vac\u00eda, agregando la clase a vttree 4. Esto rompe las suposiciones del programador HFSC de que solo las clases no vac\u00edas est\u00e1n en vttree 5. M\u00e1s tarde, cuando se destruye la clase, esto puede llevar a un Use-After-Free La soluci\u00f3n agrega una segunda verificaci\u00f3n de longitud de cola despu\u00e9s de qdisc_peek_len() para verificar que la cola no se haya vaciado."}], "id": "CVE-2025-37797", "lastModified": "2025-11-06T20:48:20.637", "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": "nvd@nist.gov", "type": "Primary"}]}, "published": "2025-05-02T15:15:48.557", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/20d584a33e480ae80d105f43e0e7b56784da41b9"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/28b09a067831f7317c3841812276022d6c940677"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/39b9095dd3b55d9b2743df038c32138efa34a9de"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/3aa852e3605000d5c47035c3fc3a986d14ccfa9f"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/3df275ef0a6ae181e8428a6589ef5d5231e58b5c"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/86cd4641c713455a4f1c8e54c370c598c2b1cee0"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/bb583c88d23b72d8d16453d24856c99bd93dadf5"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/fcc8ede663569c704fb00a702973bd6c00373283"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Mailing List", "Third Party Advisory"], "url": "https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Mailing List", "Third Party Advisory"], "url": "https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-416"}], "source": "nvd@nist.gov", "type": "Primary"}]}

{"bugzilla": {"description": "kernel: net_sched: hfsc: Fix a UAF vulnerability in class handling", "id": "2363672", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2363672"}, "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-416", "details": ["In the Linux kernel, the following vulnerability has been resolved:\nnet_sched: hfsc: Fix a UAF vulnerability in class handling\nThis patch fixes a Use-After-Free vulnerability in the HFSC qdisc class\nhandling. The issue occurs due to a time-of-check/time-of-use condition\nin hfsc_change_class() when working with certain child qdiscs like netem\nor codel.\nThe vulnerability works as follows:\n1. hfsc_change_class() checks if a class has packets (q.qlen != 0)\n2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g.,\ncodel, netem) might drop packets and empty the queue\n3. The code continues assuming the queue is still non-empty, adding\nthe class to vttree\n4. This breaks HFSC scheduler assumptions that only non-empty classes\nare in vttree\n5. Later, when the class is destroyed, this can lead to a Use-After-Free\nThe fix adds a second queue length check after qdisc_peek_len() to verify\nthe queue wasn't emptied."], "mitigation": {"lang": "en:us", "value": "To mitigate this issue, prevent module sch_hfsc from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically."}, "name": "CVE-2025-37797", "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": "Out of support scope", "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": "2025-05-02T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2025-37797\nhttps://nvd.nist.gov/vuln/detail/CVE-2025-37797\nhttps://lore.kernel.org/linux-cve-announce/2025050210-CVE-2025-37797-2aab@gregkh/T"], "statement": "The bug could happen only when qdisc with child qdiscs like netem or codel being used.", "threat_severity": "Moderate"}

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