CVE-2025-38457
Estado: ModificadaMedia (5.5)—
In the Linux kernel, the following vulnerability has been resolved:
net/sched: Abort __tc_modify_qdisc if parent class does not exist
Lion's patch [1] revealed an ancient bug in the qdisc API. Whenever a user creates/modifies a qdisc specifying as a parent another qdisc, the qdisc API will, during grafting, detect that the user is not trying to attach to a class and reject. However grafting is performed after qdisc_create (and thus the qdiscs' init callback) is executed. In qdiscs that eventually call qdisc_tree_reduce_backlog during init or change (such as fq, hhf, choke, etc), an issue arises. For example, executing the following commands:
Leer descripción completaMostrar menos
sudo tc qdisc add dev lo root handle a: htb default 2 sudo tc qdisc add dev lo parent a: handle beef fq
Qdiscs such as fq, hhf, choke, etc unconditionally invoke qdisc_tree_reduce_backlog() in their control path init() or change() which then causes a failure to find the child class; however, that does not stop the unconditional invocation of the assumed child qdisc's qlen_notify with a null class. All these qdiscs make the assumption that class is non-null.
The solution is ensure that qdisc_leaf() which looks up the parent class, and is invoked prior to qdisc_create(), should return failure on not finding the class. In this patch, we leverage qdisc_leaf to return ERR_PTRs whenever the parentid doesn't correspond to a class, so that we can detect it earlier on and abort before qdisc_create is called.
[1] https://lore.kernel.org/netdev/d912cbd7-193b-4269-9857-525bee8bbb6a@gmail.com/
CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- Puntuación base: 5.5
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.17%
- Percentil entre todas las CVEs puntuadas: 6
- Fecha de la puntuación: 3/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
Tecnologías afectadas (2)
CWE
- NVD-CWE-noinfo
Referencias
- https://git.kernel.org/stable/c/23c165dde88eac405eebb59051ea1fe139a45803
- https://git.kernel.org/stable/c/25452638f133ac19d75af3f928327d8016952c8e
- https://git.kernel.org/stable/c/4c691d1b6b6dbd73f30ed9ee7da05f037b0c49af
- https://git.kernel.org/stable/c/8ecd651ef24ab50123692a4e3e25db93cb11602a
- https://git.kernel.org/stable/c/90436e72c9622c2f70389070088325a3232d339f
- https://git.kernel.org/stable/c/923a276c74e25073ae391e930792ac86a9f77f1e
- https://git.kernel.org/stable/c/e28a383d6485c3bb51dc5953552f76c4dea33eea
- https://git.kernel.org/stable/c/ffdde7bf5a439aaa1955ebd581f5c64ab1533963
- https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
- https://cert-portal.siemens.com/productcert/html/ssa-082556.html
JSON original (NVD)
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: Abort __tc_modify_qdisc if parent class does not exist\n\nLion's patch [1] revealed an ancient bug in the qdisc API.\nWhenever a user creates/modifies a qdisc specifying as a parent another\nqdisc, the qdisc API will, during grafting, detect that the user is\nnot trying to attach to a class and reject. However grafting is\nperformed after qdisc_create (and thus the qdiscs' init callback) is\nexecuted. In qdiscs that eventually call qdisc_tree_reduce_backlog\nduring init or change (such as fq, hhf, choke, etc), an issue\narises. For example, executing the following commands:\n\nsudo tc qdisc add dev lo root handle a: htb default 2\nsudo tc qdisc add dev lo parent a: handle beef fq\n\nQdiscs such as fq, hhf, choke, etc unconditionally invoke\nqdisc_tree_reduce_backlog() in their control path init() or change() which\nthen causes a failure to find the child class; however, that does not stop\nthe unconditional invocation of the assumed child qdisc's qlen_notify with\na null class. All these qdiscs make the assumption that class is non-null.\n\nThe solution is ensure that qdisc_leaf() which looks up the parent\nclass, and is invoked prior to qdisc_create(), should return failure on\nnot finding the class.\nIn this patch, we leverage qdisc_leaf to return ERR_PTRs whenever the\nparentid doesn't correspond to a class, so that we can detect it\nearlier on and abort before qdisc_create is called.\n\n[1] https://lore.kernel.org/netdev/d912cbd7-193b-4269-9857-525bee8bbb6a@gmail.com/"
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"value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: net/sched: Abort __tc_modify_qdisc si la clase padre no existe. El parche de Lion [1] reveló un error antiguo en la API de qdisc. Siempre que un usuario crea o modifica una qdisc que especifica otra qdisc como padre, la API de qdisc detecta, durante el injerto, que el usuario no intenta asociarse a una clase y lo rechaza. Sin embargo, el injerto se realiza después de ejecutar qdisc_create (y, por lo tanto, la devolución de llamada de inicio de la qdisc). En las qdisc que eventualmente llaman a qdisc_tree_reduce_backlog durante la inicialización o el cambio (como fq, hhf, choke, etc.), surge un problema. Por ejemplo, al ejecutar los siguientes comandos: sudo tc qdisc add dev lo root handle a: htb default 2 sudo tc qdisc add dev lo parent a: handle beef fq Las Qdisc como fq, hhf, choke, etc., invocan incondicionalmente qdisc_tree_reduce_backlog() en su ruta de control init() o change(), lo que provoca un error al no encontrar la clase hija; sin embargo, esto no detiene la invocación incondicional de qlen_notify de la qdisc hija asumida con una clase nula. Todas estas qdisc asumen que la clase no es nula. La solución es garantizar que qdisc_leaf(), que busca la clase padre y se invoca antes que qdisc_create(), devuelva un error al no encontrar la clase. En este parche, aprovechamos qdisc_leaf para devolver ERR_PTR siempre que el parentid no corresponda a una clase, de modo que podamos detectarlo antes y abortar antes de que se llame a qdisc_create. [1] https://lore.kernel.org/netdev/d912cbd7-193b-4269-9857-525bee8bbb6a@gmail.com/"
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