VulnerabilityPublished 28 Jul 2025Updated 5 Nov 2026

CVE-2025-38468: Linux kernel · net/sched: Return NULL when htb_lookup_leaf encounters an empty rbtree

Affects Linux kernelSource CVE Database V5

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Not known to be exploited · fixed in fed3570e548a6c9f95c5f4c9e1a7afc1679fd90d : update Linux kernel when convenient.

Data as of 5 Nov 2026, 21:19 UTC

Severity

Unrated

Rated by Threat Radar · No CVSS score from NVD or the CNA

Thin evidence

One scorer or none

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact: Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-11-05.

Patch

Available – fixed in fed3570e548a6c9f95c5f4c9e1a7afc1679fd90d, e5c480dc62a3025b8428d4818e722da30ad6804f, 850226aef8d28a00cf966ef26d2f8f2bff344535 +5

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Jul 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 512bb43eb5422ee69a1be05ea0d89dc074fac9a2, < fed3570e548a6c9f95c5f4c9e1a7afc1679fd90d	Fixed in fed3570e548a6c9f95c5f4c9e1a7afc1679fd90d
LinuxLinux	Affected ≥ 512bb43eb5422ee69a1be05ea0d89dc074fac9a2, < e5c480dc62a3025b8428d4818e722da30ad6804f	Fixed in e5c480dc62a3025b8428d4818e722da30ad6804f
LinuxLinux	Affected ≥ 512bb43eb5422ee69a1be05ea0d89dc074fac9a2, < 850226aef8d28a00cf966ef26d2f8f2bff344535	Fixed in 850226aef8d28a00cf966ef26d2f8f2bff344535
LinuxLinux	Affected ≥ 512bb43eb5422ee69a1be05ea0d89dc074fac9a2, < 3691f84269a23f7edd263e9b6edbc27b7ae332f4	Fixed in 3691f84269a23f7edd263e9b6edbc27b7ae332f4
LinuxLinux	Affected ≥ 512bb43eb5422ee69a1be05ea0d89dc074fac9a2, < 890a5d423ef0a7bd13447ceaffad21189f557301	Fixed in 890a5d423ef0a7bd13447ceaffad21189f557301
LinuxLinux	Affected ≥ 512bb43eb5422ee69a1be05ea0d89dc074fac9a2, < 7ff2d83ecf2619060f30ecf9fad4f2a700fca344	Fixed in 7ff2d83ecf2619060f30ecf9fad4f2a700fca344

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/

References

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