{
  "threat_severity" : "Moderate",
  "public_date" : "2025-07-28T00:00:00Z",
  "bugzilla" : {
    "description" : "kernel: net/sched: Return NULL when htb_lookup_leaf encounters an empty rbtree",
    "id" : "2383913",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2383913"
  },
  "cvss3" : {
    "cvss3_base_score" : "5.5",
    "cvss3_scoring_vector" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
    "status" : "verified"
  },
  "cwe" : "CWE-754",
  "details" : [ "In the Linux kernel, the following vulnerability has been resolved:\nnet/sched: Return NULL when htb_lookup_leaf encounters an empty rbtree\nhtb_lookup_leaf has a BUG_ON that can trigger with the following:\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 htb rate 64bit\ntc qdisc add dev lo parent 1:1 handle 2: netem\ntc qdisc add dev lo parent 2:1 handle 3: blackhole\nping -I lo -c1 -W0.001 127.0.0.1\nThe root cause is the following:\n1. htb_dequeue calls htb_dequeue_tree which calls the dequeue handler on\nthe selected leaf qdisc\n2. netem_dequeue calls enqueue on the child qdisc\n3. blackhole_enqueue drops the packet and returns a value that is not\njust NET_XMIT_SUCCESS\n4. Because of this, netem_dequeue calls qdisc_tree_reduce_backlog, and\nsince qlen is now 0, it calls htb_qlen_notify -> htb_deactivate ->\nhtb_deactiviate_prios -> htb_remove_class_from_row -> htb_safe_rb_erase\n5. As this is the only class in the selected hprio rbtree,\n__rb_change_child in __rb_erase_augmented sets the rb_root pointer to\nNULL\n6. Because blackhole_dequeue returns NULL, netem_dequeue returns NULL,\nwhich causes htb_dequeue_tree to call htb_lookup_leaf with the same\nhprio rbtree, and fail the BUG_ON\nThe function graph for this scenario is shown here:\n0)               |  htb_enqueue() {\n0) + 13.635 us   |    netem_enqueue();\n0)   4.719 us    |    htb_activate_prios();\n0) # 2249.199 us |  }\n0)               |  htb_dequeue() {\n0)   2.355 us    |    htb_lookup_leaf();\n0)               |    netem_dequeue() {\n0) + 11.061 us   |      blackhole_enqueue();\n0)               |      qdisc_tree_reduce_backlog() {\n0)               |        qdisc_lookup_rcu() {\n0)   1.873 us    |          qdisc_match_from_root();\n0)   6.292 us    |        }\n0)   1.894 us    |        htb_search();\n0)               |        htb_qlen_notify() {\n0)   2.655 us    |          htb_deactivate_prios();\n0)   6.933 us    |        }\n0) + 25.227 us   |      }\n0)   1.983 us    |      blackhole_dequeue();\n0) + 86.553 us   |    }\n0) # 2932.761 us |    qdisc_warn_nonwc();\n0)               |    htb_lookup_leaf() {\n0)               |      BUG_ON();\n------------------------------------------\nThe full original bug report can be seen here [1].\nWe can fix this just by returning NULL instead of the BUG_ON,\nas htb_dequeue_tree returns NULL when htb_lookup_leaf returns\nNULL.\n[1] https://lore.kernel.org/netdev/pF5XOOIim0IuEfhI-SOxTgRvNoDwuux7UHKnE_Y5-zVd4wmGvNk2ceHjKb8ORnzw0cGwfmVu42g9dL7XyJLf1NEzaztboTWcm0Ogxuojoeo=@willsroot.io/" ],
  "statement" : "This is denial-of-service vulnerability in htb_lookup_leaf() within the Linux kernel's traffic control (net/sched) subsystem. A local attacker with CAP_NET_ADMIN (e.g., via unprivileged user namespaces) can trigger a kernel panic by manipulating qdisc trees using tc, causing a BUG_ON due to an empty red-black tree.",
  "affected_release" : [ {
    "product_name" : "Red Hat Enterprise Linux 10",
    "release_date" : "2025-11-11T00:00:00Z",
    "advisory" : "RHSA-2025:20095",
    "cpe" : "cpe:/o:redhat:enterprise_linux:10.1",
    "package" : "kernel-0:6.12.0-124.8.1.el10_1"
  } ],
  "package_state" : [ {
    "product_name" : "Red Hat Enterprise Linux 6",
    "fix_state" : "Out of support scope",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Out of support scope",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Out of support scope",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8",
    "fix_state" : "Fix deferred",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8",
    "fix_state" : "Fix deferred",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "fix_state" : "Fix deferred",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "fix_state" : "Fix deferred",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9"
  } ],
  "references" : [ "https://www.cve.org/CVERecord?id=CVE-2025-38468\nhttps://nvd.nist.gov/vuln/detail/CVE-2025-38468\nhttps://lore.kernel.org/linux-cve-announce/2025072834-CVE-2025-38468-4110@gregkh/T" ],
  "name" : "CVE-2025-38468",
  "mitigation" : {
    "value" : "To mitigate this issue, prevent module sch_htb from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically.",
    "lang" : "en:us"
  },
  "csaw" : false
}