CVE-2026-23074 (GCVE-0-2026-23074)
Vulnerability from cvelistv5 – Published: 2026-02-04 16:07 – Updated: 2026-02-09 08:38
VLAI?
Title
net/sched: Enforce that teql can only be used as root qdisc
Summary
In the Linux kernel, the following vulnerability has been resolved:
net/sched: Enforce that teql can only be used as root qdisc
Design intent of teql is that it is only supposed to be used as root qdisc.
We need to check for that constraint.
Although not important, I will describe the scenario that unearthed this
issue for the curious.
GangMin Kim <km.kim1503@gmail.com> managed to concot a scenario as follows:
ROOT qdisc 1:0 (QFQ)
├── class 1:1 (weight=15, lmax=16384) netem with delay 6.4s
└── class 1:2 (weight=1, lmax=1514) teql
GangMin sends a packet which is enqueued to 1:1 (netem).
Any invocation of dequeue by QFQ from this class will not return a packet
until after 6.4s. In the meantime, a second packet is sent and it lands on
1:2. teql's enqueue will return success and this will activate class 1:2.
Main issue is that teql only updates the parent visible qlen (sch->q.qlen)
at dequeue. Since QFQ will only call dequeue if peek succeeds (and teql's
peek always returns NULL), dequeue will never be called and thus the qlen
will remain as 0. With that in mind, when GangMin updates 1:2's lmax value,
the qfq_change_class calls qfq_deact_rm_from_agg. Since the child qdisc's
qlen was not incremented, qfq fails to deactivate the class, but still
frees its pointers from the aggregate. So when the first packet is
rescheduled after 6.4 seconds (netem's delay), a dangling pointer is
accessed causing GangMin's causing a UAF.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
| Vendor | Product | Version | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux |
Affected:
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 73d970ff0eddd874a84c953387c7f4464b705fc6
(git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < ae810e6a8ac4fe25042e6825d2a401207a2e41fb (git) Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < dad49a67c2d817bfec98e6e45121b351e3a0202c (git) Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 0686bedfed34155520f3f735cbf3210cb9044380 (git) Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 4c7e8aa71c9232cba84c289b4b56cba80b280841 (git) Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 16ed73c1282d376b956bff23e5139add061767ba (git) Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 50da4b9d07a7a463e2cfb738f3ad4cff6b2c9c3b (git) |
|||||||
|
|||||||||
{
"containers": {
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{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"net/sched/sch_teql.c"
],
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],
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"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.10.*",
"status": "unaffected",
"version": "5.10.249",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.199",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.162",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.122",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.68",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.8",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "6.19",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
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{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.18.8",
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},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"descriptions": [
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"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: Enforce that teql can only be used as root qdisc\n\nDesign intent of teql is that it is only supposed to be used as root qdisc.\nWe need to check for that constraint.\n\nAlthough not important, I will describe the scenario that unearthed this\nissue for the curious.\n\nGangMin Kim \u003ckm.kim1503@gmail.com\u003e managed to concot a scenario as follows:\n\nROOT qdisc 1:0 (QFQ)\n \u251c\u2500\u2500 class 1:1 (weight=15, lmax=16384) netem with delay 6.4s\n \u2514\u2500\u2500 class 1:2 (weight=1, lmax=1514) teql\n\nGangMin sends a packet which is enqueued to 1:1 (netem).\nAny invocation of dequeue by QFQ from this class will not return a packet\nuntil after 6.4s. In the meantime, a second packet is sent and it lands on\n1:2. teql\u0027s enqueue will return success and this will activate class 1:2.\nMain issue is that teql only updates the parent visible qlen (sch-\u003eq.qlen)\nat dequeue. Since QFQ will only call dequeue if peek succeeds (and teql\u0027s\npeek always returns NULL), dequeue will never be called and thus the qlen\nwill remain as 0. With that in mind, when GangMin updates 1:2\u0027s lmax value,\nthe qfq_change_class calls qfq_deact_rm_from_agg. Since the child qdisc\u0027s\nqlen was not incremented, qfq fails to deactivate the class, but still\nfrees its pointers from the aggregate. So when the first packet is\nrescheduled after 6.4 seconds (netem\u0027s delay), a dangling pointer is\naccessed causing GangMin\u0027s causing a UAF."
}
],
"providerMetadata": {
"dateUpdated": "2026-02-09T08:38:13.759Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
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"references": [
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{
"url": "https://git.kernel.org/stable/c/ae810e6a8ac4fe25042e6825d2a401207a2e41fb"
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{
"url": "https://git.kernel.org/stable/c/dad49a67c2d817bfec98e6e45121b351e3a0202c"
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{
"url": "https://git.kernel.org/stable/c/0686bedfed34155520f3f735cbf3210cb9044380"
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"url": "https://git.kernel.org/stable/c/4c7e8aa71c9232cba84c289b4b56cba80b280841"
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"url": "https://git.kernel.org/stable/c/50da4b9d07a7a463e2cfb738f3ad4cff6b2c9c3b"
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"title": "net/sched: Enforce that teql can only be used as root qdisc",
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"cveId": "CVE-2026-23074",
"datePublished": "2026-02-04T16:07:59.379Z",
"dateReserved": "2026-01-13T15:37:45.958Z",
"dateUpdated": "2026-02-09T08:38:13.759Z",
"state": "PUBLISHED"
},
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"vulnerability-lookup:meta": {
"nvd": "{\"cve\":{\"id\":\"CVE-2026-23074\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-02-04T17:16:18.127\",\"lastModified\":\"2026-02-06T17:16:23.333\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nnet/sched: Enforce that teql can only be used as root qdisc\\n\\nDesign intent of teql is that it is only supposed to be used as root qdisc.\\nWe need to check for that constraint.\\n\\nAlthough not important, I will describe the scenario that unearthed this\\nissue for the curious.\\n\\nGangMin Kim \u003ckm.kim1503@gmail.com\u003e managed to concot a scenario as follows:\\n\\nROOT qdisc 1:0 (QFQ)\\n \u251c\u2500\u2500 class 1:1 (weight=15, lmax=16384) netem with delay 6.4s\\n \u2514\u2500\u2500 class 1:2 (weight=1, lmax=1514) teql\\n\\nGangMin sends a packet which is enqueued to 1:1 (netem).\\nAny invocation of dequeue by QFQ from this class will not return a packet\\nuntil after 6.4s. In the meantime, a second packet is sent and it lands on\\n1:2. teql\u0027s enqueue will return success and this will activate class 1:2.\\nMain issue is that teql only updates the parent visible qlen (sch-\u003eq.qlen)\\nat dequeue. Since QFQ will only call dequeue if peek succeeds (and teql\u0027s\\npeek always returns NULL), dequeue will never be called and thus the qlen\\nwill remain as 0. With that in mind, when GangMin updates 1:2\u0027s lmax value,\\nthe qfq_change_class calls qfq_deact_rm_from_agg. Since the child qdisc\u0027s\\nqlen was not incremented, qfq fails to deactivate the class, but still\\nfrees its pointers from the aggregate. So when the first packet is\\nrescheduled after 6.4 seconds (netem\u0027s delay), a dangling pointer is\\naccessed causing GangMin\u0027s causing a UAF.\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/0686bedfed34155520f3f735cbf3210cb9044380\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/16ed73c1282d376b956bff23e5139add061767ba\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/4c7e8aa71c9232cba84c289b4b56cba80b280841\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/50da4b9d07a7a463e2cfb738f3ad4cff6b2c9c3b\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/73d970ff0eddd874a84c953387c7f4464b705fc6\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/ae810e6a8ac4fe25042e6825d2a401207a2e41fb\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/dad49a67c2d817bfec98e6e45121b351e3a0202c\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
}
}
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Sightings
| Author | Source | Type | Date |
|---|
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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