CVE-2025-38468 (GCVE-0-2025-38468)

Vulnerability from cvelistv5 – Published: 2025-07-28 11:12 – Updated: 2026-05-12 12:05
VLAI
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
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted 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)
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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)
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Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.5 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP Affected: V3.1.5 , < * (custom)
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Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.5 , < * (custom)
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    "nvd": "{\"cve\":{\"id\":\"CVE-2025-38468\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-07-28T12:15:28.503\",\"lastModified\":\"2026-05-12T13:16:50.353\",\"vulnStatus\":\"Modified\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"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/\"},{\"lang\":\"es\",\"value\":\"En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: net/sched: Devuelve NULL cuando htb_lookup_leaf encuentra un rbtree vac\u00edo htb_lookup_leaf tiene un BUG_ON que puede activarse con lo siguiente: 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 La causa ra\u00edz es la siguiente: 1. htb_dequeue llama a htb_dequeue_tree, que llama al controlador de dequeue en el qdisc de hoja seleccionado 2. netem_dequeue llama a enqueue en el hijo qdisc 3. blackhole_enqueue descarta el paquete y devuelve un valor que no es solo NET_XMIT_SUCCESS 4. Debido a esto, netem_dequeue llama a qdisc_tree_reduce_backlog y, dado que qlen ahora es 0, llama a htb_qlen_notify -\u0026gt; htb_deactivate -\u0026gt; htb_deactiviate_prios -\u0026gt; htb_remove_class_from_row -\u0026gt; htb_safe_rb_erase 5. Como esta es la \u00fanica clase en el rbtree hprio seleccionado, __rb_change_child en __rb_erase_augmented establece el puntero rb_root en NULL 6. Debido a que blackhole_dequeue devuelve NULL, netem_dequeue devuelve NULL, lo que hace que htb_dequeue_tree llame a htb_lookup_leaf con el mismo rbtree hprio y falle el BUG_ON Se muestra el gr\u00e1fico de funciones para este escenario aqu\u00ed: 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/\"}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H\",\"baseScore\":5.5,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.8,\"impactScore\":3.6}]},\"weaknesses\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-476\"}]}],\"configurations\":[{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"2.6.29\",\"versionEndExcluding\":\"5.4.297\",\"matchCriteriaId\":\"B9F2FDF6-4EB5-4DFF-BC93-F12605A32B6E\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"5.5\",\"versionEndExcluding\":\"5.10.241\",\"matchCriteriaId\":\"D0D21C35-EB8A-488A-BBF9-403E4817E5DD\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"5.11\",\"versionEndExcluding\":\"5.15.190\",\"matchCriteriaId\":\"AD9E597F-3DDE-4D7E-976C-463D0611F13F\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"5.16\",\"versionEndExcluding\":\"6.1.147\",\"matchCriteriaId\":\"A4FD62FC-0DAE-4ACE-8C9C-66156518C3E1\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.2\",\"versionEndExcluding\":\"6.6.100\",\"matchCriteriaId\":\"094B81E0-B756-4727-85CA-F3F8D1C9D116\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.7\",\"versionEndExcluding\":\"6.12.40\",\"matchCriteriaId\":\"0099D5A4-B157-4D36-8858-982C7D579030\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.13\",\"versionEndExcluding\":\"6.15.8\",\"matchCriteriaId\":\"C7AFE5B0-F3B1-4D30-B8BF-EDA0385C4746\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:6.16:rc1:*:*:*:*:*:*\",\"matchCriteriaId\":\"6D4894DB-CCFE-4602-B1BF-3960B2E19A01\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:6.16:rc2:*:*:*:*:*:*\",\"matchCriteriaId\":\"09709862-E348-4378-8632-5A7813EDDC86\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:6.16:rc3:*:*:*:*:*:*\",\"matchCriteriaId\":\"415BF58A-8197-43F5-B3D7-D1D63057A26E\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:6.16:rc4:*:*:*:*:*:*\",\"matchCriteriaId\":\"A0517869-312D-4429-80C2-561086E1421C\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:6.16:rc5:*:*:*:*:*:*\",\"matchCriteriaId\":\"85421F4E-C863-4ABF-B4B4-E887CC2F7F92\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:6.16:rc6:*:*:*:*:*:*\",\"matchCriteriaId\":\"3827F0D4-5FEE-4181-B267-5A45E7CA11FC\"}]}]},{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*\",\"matchCriteriaId\":\"FA6FEEC2-9F11-4643-8827-749718254FED\"}]}]}],\"references\":[{\"url\":\"https://git.kernel.org/stable/c/0e1d5d9b5c5966e2e42e298670808590db5ed628\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/3691f84269a23f7edd263e9b6edbc27b7ae332f4\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/5c0506cd1b1a3b145bda2612bbf7fe78d186c355\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/7ff2d83ecf2619060f30ecf9fad4f2a700fca344\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/850226aef8d28a00cf966ef26d2f8f2bff344535\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/890a5d423ef0a7bd13447ceaffad21189f557301\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/e5c480dc62a3025b8428d4818e722da30ad6804f\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/fed3570e548a6c9f95c5f4c9e1a7afc1679fd90d\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Third Party Advisory\"]},{\"url\":\"https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Third Party Advisory\"]},{\"url\":\"https://cert-portal.siemens.com/productcert/html/ssa-082556.html\",\"source\":\"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e\"}]}}"
  }
}


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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

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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.


Detection rules are retrieved from Rulezet.