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EUVD-2026-336342
European Vulnerability Database identifier assigned by ENISAReserved
2026-10-02 07:51
Assigner
ENISA
Alias of
a CVE record, shown under related vulnerabilities.
This identifier carries no description, severity or references of its own:
they belong to that CVE.
{
"assigner": "ENISA",
"date_reserved": "2026-10-02T07:51:56.715661+00:00",
"id": "EUVD-2026-336342"
}
CVE-2025-38468 (GCVE-0-2025-38468)
Vulnerability from cvelistv5 – Published: 2025-07-28 11:12 – Updated: 2026-07-14 12:42
VLAI
EPSS
VEX
Title
net/sched: Return NULL when htb_lookup_leaf encounters an empty rbtree
Summary
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/
Severity
No CVSS data available.
Assigner
References
11 references
Impacted products
5 products
| Vendor | Product | Version | |
|---|---|---|---|
| Linux | Linux |
Affected:
512bb43eb5422ee69a1be05ea0d89dc074fac9a2 , < fed3570e548a6c9f95c5f4c9e1a7afc1679fd90d
(git)
Affected: 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 , < 5c0506cd1b1a3b145bda2612bbf7fe78d186c355 (git) Affected: 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 , < 850226aef8d28a00cf966ef26d2f8f2bff344535 (git) Affected: 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 , < 890a5d423ef0a7bd13447ceaffad21189f557301 (git) Affected: 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 , < 7ff2d83ecf2619060f30ecf9fad4f2a700fca344 (git) Affected: 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 , < e5c480dc62a3025b8428d4818e722da30ad6804f (git) Affected: 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 , < 3691f84269a23f7edd263e9b6edbc27b7ae332f4 (git) Affected: 512bb43eb5422ee69a1be05ea0d89dc074fac9a2 , < 0e1d5d9b5c5966e2e42e298670808590db5ed628 (git) |
|
| Linux | Linux |
Affected:
2.6.29
Unaffected: 0 , < 2.6.29 (semver) Unaffected: 5.4.297 , ≤ 5.4.* (semver) Unaffected: 5.10.241 , ≤ 5.10.* (semver) Unaffected: 5.15.190 , ≤ 5.15.* (semver) Unaffected: 6.1.147 , ≤ 6.1.* (semver) Unaffected: 6.6.100 , ≤ 6.6.* (semver) Unaffected: 6.12.40 , ≤ 6.12.* (semver) Unaffected: 6.15.8 , ≤ 6.15.* (semver) Unaffected: 6.16 , ≤ * (original_commit_for_fix) |
|
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP |
Affected:
V3.1.5 , < *
(custom)
|
|
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP |
Affected:
V3.1.5 , < *
(custom)
|
|
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP |
Affected:
V3.1.5 , < *
(custom)
|
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: Return NULL when htb_lookup_leaf encounters an empty rbtree\n\nhtb_lookup_leaf has a BUG_ON that can trigger with the following:\n\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\n\nThe root cause is the following:\n\n1. htb_dequeue calls htb_dequeue_tree which calls the dequeue handler on\n the 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\n just NET_XMIT_SUCCESS\n4. Because of this, netem_dequeue calls qdisc_tree_reduce_backlog, and\n since qlen is now 0, it calls htb_qlen_notify -\u003e htb_deactivate -\u003e\n htb_deactiviate_prios -\u003e htb_remove_class_from_row -\u003e 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\n NULL\n6. Because blackhole_dequeue returns NULL, netem_dequeue returns NULL,\n which causes htb_dequeue_tree to call htb_lookup_leaf with the same\n hprio rbtree, and fail the BUG_ON\n\nThe function graph for this scenario is shown here:\n 0) | htb_enqueue() {\n 0) + 13.635 us | netem_enqueue();\n 0) 4.719 us | htb_activate_prios();\n 0) # 2249.199 us | }\n 0) | htb_dequeue() {\n 0) 2.355 us | htb_lookup_leaf();\n 0) | netem_dequeue() {\n 0) + 11.061 us | blackhole_enqueue();\n 0) | qdisc_tree_reduce_backlog() {\n 0) | qdisc_lookup_rcu() {\n 0) 1.873 us | qdisc_match_from_root();\n 0) 6.292 us | }\n 0) 1.894 us | htb_search();\n 0) | htb_qlen_notify() {\n 0) 2.655 us | htb_deactivate_prios();\n 0) 6.933 us | }\n 0) + 25.227 us | }\n 0) 1.983 us | blackhole_dequeue();\n 0) + 86.553 us | }\n 0) # 2932.761 us | qdisc_warn_nonwc();\n 0) | htb_lookup_leaf() {\n 0) | BUG_ON();\n ------------------------------------------\n\nThe full original bug report can be seen here [1].\n\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\n[1] https://lore.kernel.org/netdev/pF5XOOIim0IuEfhI-SOxTgRvNoDwuux7UHKnE_Y5-zVd4wmGvNk2ceHjKb8ORnzw0cGwfmVu42g9dL7XyJLf1NEzaztboTWcm0Ogxuojoeo=@willsroot.io/"
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Trend slope:
-
(linear fit over daily sighting counts)
Show additional events:
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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