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net_sched: hfsc: Fix a UAF vulnerability in class handling

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: net_sched: hfsc: Fix a UAF vulnerability in class handling This patch fixes a Use-After-Free vulnerability in the HFSC qdisc class handling. The issue occurs due to a time-of-check/time-of-use condition in hfsc_change_class() when working with certain child qdiscs like netem or codel. The vulnerability works as follows: 1. hfsc_change_class() checks if a class has packets (q.qlen != 0) 2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g., codel, netem) might drop packets and empty the queue 3. The code continues assuming the queue is still non-empty, adding the class to vttree 4. This breaks HFSC scheduler assumptions that only non-empty classes are in vttree 5. Later, when the class is destroyed, this can lead to a Use-After-Free The fix adds a second queue length check after qdisc_peek_len() to verify the queue wasn't emptied.

Products
Kernel
Affected versions
Not specified
Fixed versions
5.10.237, 5.15.181, 5.4.293, 6.1.136, 6.12.26, 6.14.5, 6.6.89
CVEs
CVE-2025-37797
Confirmed fixed CVEs
Not specified
Updated in this feed
4 Nov 2026, 11:57 UTC · Revision 1

Source evidence

net_sched: hfsc: Fix a UAF vulnerability in class handling

core-osv · Original source

Published 2 May 2025, 14:16 UTC

In the Linux kernel, the following vulnerability has been resolved: net_sched: hfsc: Fix a UAF vulnerability in class handling This patch fixes a Use-After-Free vulnerability in the HFSC qdisc class handling. The issue occurs due to a time-of-check/time-of-use condition in hfsc_change_class() when working with certain child qdiscs like netem or codel. The vulnerability works as follows: 1. hfsc_change_class() checks if a class has packets (q.qlen != 0) 2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g., codel, netem) might drop packets and empty the queue 3. The code continues assuming the queue is still non-empty, adding the class to vttree 4. This breaks HFSC scheduler assumptions that only non-empty classes are in vttree 5. Later, when the class is destroyed, this can lead to a Use-After-Free The fix adds a second queue length check after qdisc_peek_len() to verify the queue wasn't emptied.

osv:CVE-2025-37797

Kernel

Fixed versions: 5.4.293, 5.10.237, 5.15.181, 6.1.136, 6.6.89, 6.12.26, 6.14.5

Complete source record
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  "url": "https://osv.dev/vulnerability/CVE-2025-37797",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net_sched: hfsc: Fix a UAF vulnerability in class handling",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net_sched: hfsc: Fix a UAF vulnerability in class handling This patch fixes a Use-After-Free vulnerability in the HFSC qdisc class handling. The issue occurs due to a time-of-check/time-of-use condition in hfsc_change_class() when working with certain child qdiscs like netem or codel. The vulnerability works as follows: 1. hfsc_change_class() checks if a class has packets (q.qlen != 0) 2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g., codel, netem) might drop packets and empty the queue 3. The code continues assuming the queue is still non-empty, adding the class to vttree 4. This breaks HFSC scheduler assumptions that only non-empty classes are in vttree 5. Later, when the class is destroyed, this can lead to a Use-After-Free The fix adds a second queue length check after qdisc_peek_len() to verify the queue wasn't emptied.",
    "evidence": "osv:CVE-2025-37797",
    "products": [
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      "modified": "2026-10-28T02:30:35.073831532Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/20d584a33e480ae80d105f43e0e7b56784da41b9",
        "https://git.kernel.org/stable/c/28b09a067831f7317c3841812276022d6c940677",
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        "https://git.kernel.org/stable/c/fcc8ede663569c704fb00a702973bd6c00373283",
        "https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html",
        "https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/37xxx/CVE-2025-37797.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-37797",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/37xxx/CVE-2025-37797.json"
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    "related_cves": [
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  "source_id": "core-osv",
  "document_id": 502212,
  "published_at": "2025-05-02T14:16:01.905+00:00"
}