{
  "threat_severity" : "Moderate",
  "public_date" : "2025-09-11T00:00:00Z",
  "bugzilla" : {
    "description" : "kernel: net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit",
    "id" : "2394648",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2394648"
  },
  "cvss3" : {
    "cvss3_base_score" : "7.3",
    "cvss3_scoring_vector" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H",
    "status" : "verified"
  },
  "cwe" : "CWE-390",
  "details" : [ "In the Linux kernel, the following vulnerability has been resolved:\nnet/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit\nThe following setup can trigger a WARNING in htb_activate due to\nthe condition: !cl->leaf.q->q.qlen\ntc qdisc del dev lo root\ntc qdisc add dev lo root handle 1: htb default 1\ntc class add dev lo parent 1: classid 1:1 \\\nhtb rate 64bit\ntc qdisc add dev lo parent 1:1 handle f: \\\ncake memlimit 1b\nping -I lo -f -c1 -s64 -W0.001 127.0.0.1\nThis is because the low memlimit leads to a low buffer_limit, which\ncauses packet dropping. However, cake_enqueue still returns\nNET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an\nempty child qdisc. We should return NET_XMIT_CN when packets are\ndropped from the same tin and flow.\nI do not believe return value of NET_XMIT_CN is necessary for packet\ndrops in the case of ack filtering, as that is meant to optimize\nperformance, not to signal congestion." ],
  "affected_release" : [ {
    "product_name" : "Red Hat Enterprise Linux 10",
    "release_date" : "2026-04-21T00:00:00Z",
    "advisory" : "RHSA-2026:9264",
    "cpe" : "cpe:/o:redhat:enterprise_linux:10.1",
    "package" : "kernel-0:6.12.0-124.52.1.el10_1"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "release_date" : "2026-04-20T00:00:00Z",
    "advisory" : "RHSA-2026:8921",
    "cpe" : "cpe:/a:redhat:enterprise_linux:9",
    "package" : "kernel-0:5.14.0-611.49.1.el9_7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "release_date" : "2026-04-20T00:00:00Z",
    "advisory" : "RHSA-2026:8921",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9",
    "package" : "kernel-0:5.14.0-611.49.1.el9_7"
  } ],
  "package_state" : [ {
    "product_name" : "Red Hat Enterprise Linux 6",
    "fix_state" : "Not affected",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Not affected",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Not affected",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8",
    "fix_state" : "Not affected",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8",
    "fix_state" : "Not affected",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "fix_state" : "Affected",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9"
  } ],
  "references" : [ "https://www.cve.org/CVERecord?id=CVE-2025-39766\nhttps://nvd.nist.gov/vuln/detail/CVE-2025-39766\nhttps://lore.kernel.org/linux-cve-announce/2025091144-CVE-2025-39766-7465@gregkh/T" ],
  "name" : "CVE-2025-39766",
  "csaw" : false
}