Intel

CVE-2025-38468

Siemens ProductCERT Advisory SSA-082556

noneEPSS 0.2%

Description

In the Linux kernel, the following vulnerability has been resolved:

net/sched: Return NULL when htb_lookup_leaf encounters an empty rbtree

htb_lookup_leaf has a BUG_ON that can trigger with the following:

tc qdisc del dev lo root tc qdisc add dev lo root handle 1: htb default 1 tc class add dev lo parent 1: classid 1:1 htb rate 64bit tc qdisc add dev lo parent 1:1 handle 2: netem tc qdisc add dev lo parent 2:1 handle 3: blackhole ping -I lo -c1 -W0.001 127.0.0.1

The root cause is the following:

  1. htb_dequeue calls htb_dequeue_tree which calls the dequeue handler on the selected leaf qdisc
  2. netem_dequeue calls enqueue on the child qdisc
  3. blackhole_enqueue drops the packet and returns a value that is not just NET_XMIT_SUCCESS
  4. Because of this, netem_dequeue calls qdisc_tree_reduce_backlog, and since qlen is now 0, it calls htb_qlen_notify -> htb_deactivate -> htb_deactiviate_prios -> htb_remove_class_from_row -> htb_safe_rb_erase
  5. As this is the only class in the selected hprio rbtree, __rb_change_child in __rb_erase_augmented sets the rb_root pointer to NULL
  6. Because blackhole_dequeue returns NULL, netem_dequeue returns NULL, which causes htb_dequeue_tree to call htb_lookup_leaf with the same hprio rbtree, and fail the BUG_ON

The function graph for this scenario is shown here: 0) | htb_enqueue() { 0) + 13.635 us | netem_enqueue(); 0) 4.719 us | htb_activate_prios(); 0) # 2249.199 us | } 0) | htb_dequeue() { 0) 2.355 us | htb_lookup_leaf(); 0) | netem_dequeue() { 0) + 11.061 us | blackhole_enqueue(); 0) | qdisc_tree_reduce_backlog() { 0) | qdisc_lookup_rcu() { 0) 1.873 us | qdisc_match_from_root(); 0) 6.292 us | } 0) 1.894 us | htb_search(); 0) | htb_qlen_notify() { 0) 2.655 us | htb_deactivate_prios(); 0) 6.933 us | } 0) + 25.227 us | } 0) 1.983 us | blackhole_dequeue(); 0) + 86.553 us | } 0) # 2932.761 us | qdisc_warn_nonwc(); 0) | htb_lookup_leaf() { 0) | BUG_ON();

The full original bug report can be seen here [1].

We can fix this just by returning NULL instead of the BUG_ON, as htb_dequeue_tree returns NULL when htb_lookup_leaf returns NULL.

[1] https://lore.kernel.org/netdev/pF5XOOIim0IuEfhI-SOxTgRvNoDwuux7UHKnE_Y5-zVd4wmGvNk2ceHjKb8ORnzw0cGwfmVu42g9dL7XyJLf1NEzaztboTWcm0Ogxuojoeo=@willsroot.io/

Source: SIEMENS_ADVISORYBSIBSI_CSAFCVELISTV5EUVDCVEORG

Metrics

Severity
none
Priority score
212.97
KEV status
—
Exploit maturity
no public PoC known
XIEM Effective CVSS
—
CVSS v3
0.0
CVSS v4
—
EPSS percentile
5.9 %
Low — this CVE sits in the lower 10% of all CVEs scored today.
EPSS score
0.2 %
Low — model estimates < 1% exploitation likelihood.
Published
2021-09-26 00:00 UTC
CWE
—

Affected operating systems

  • bsd

    freebsd / freebsd13.2

  • bsd

    freebsd / freebsd13.3

  • bsd

    freebsd / freebsd14.0

  • bsd

    freebsd / freebsd14.1

  • bsd

    netbsd / netbsd

  • linux

    almalinux / almalinux9.0

  • linux

    amazon / amazon_linux2023.0

  • linux

    amazon / amazon_linux

  • linux

    ubuntu / awsbionic

  • linux

    ubuntu / awsjammy

  • linux

    ubuntu / awsnoble

  • linux

    ubuntu / awsresolute

  • linux

    ubuntu / awsxenial

  • linux

    ubuntu / aws-6.8jammy

  • linux

    ubuntu / aws-hwexenial

  • linux

    ubuntu / azurejammy

  • linux

    ubuntu / azurenoble

  • linux

    ubuntu / azureresolute

  • linux

    ubuntu / azurexenial

  • linux

    ubuntu / azure-4.15bionic

  • linux

    suse / basesystem_module15

  • linux

    debian / debian_linux10.0

  • linux

    debian / debian_linux11.0

  • linux

    debian / debian_linux12.0

Affected products

Products and version ranges extracted from the vendor/CERT advisory. A range like „<4.14.6“ implies the update recommendation „upgrade to 4.14.6 or later“.

  • android

    :linux_kernel::0

  • android

    :linux_kernel:Kernel

  • arista

    cloudvision_agni2024.4.0 – 2025.2.2

  • arista

    cloudvision_portal2024.2.0 – 2026.1.0

  • arista

    velocloud_edge4.5.0 – 6.4.1

  • arista

    velocloud_gateway

  • arista

    velocloud_orchestrator

  • bitnami

    java-min1.9.0

  • bitnami

    varnish6.1.0

  • bitnami

    varnish7.4.0

  • Dell

    ECS3.8.1.0-3.8.1.7

  • Dell

    NetWorkervProxy 19.14

  • Dell

    PowerScale OneFSNode Firmware Package 14.1

  • Dell

    Secure Connect GatewayAppliance 5.32.00.18

  • Dell

    Secure Connect Gateway< 5.36.00.16

    fixed in 5.36.00.16

  • Dell

    Secure Connect GatewayAppliance <5.32.00.18

  • gnu

    glibc2.35 – 2.37

  • gnu

    glibc

  • gnupg

    libgcrypt1.11.0 – 1.11.3

  • gnupg

    libgcrypt1.12.0 – 1.12.2

  • gnupg

    libgcrypt1.8.8 – 1.10.4

  • hackage

    xz-clib5.6.3

  • hackage

    xz-clib5.6.4

  • hackage

    xz-clib5.8.0

References & sources

Linked CVEs

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IDCVE-2025-38468