CVE-2024-49940 (GCVE-0-2024-49940)
Vulnerability from cvelistv5 – Published: 2024-10-21 18:01 – Updated: 2026-08-05 11:40
VLAI
EPSS
VEX
Title
l2tp: prevent possible tunnel refcount underflow
Summary
In the Linux kernel, the following vulnerability has been resolved:
l2tp: prevent possible tunnel refcount underflow
When a session is created, it sets a backpointer to its tunnel. When
the session refcount drops to 0, l2tp_session_free drops the tunnel
refcount if session->tunnel is non-NULL. However, session->tunnel is
set in l2tp_session_create, before the tunnel refcount is incremented
by l2tp_session_register, which leaves a small window where
session->tunnel is non-NULL when the tunnel refcount hasn't been
bumped.
Moving the assignment to l2tp_session_register is trivial but
l2tp_session_create calls l2tp_session_set_header_len which uses
session->tunnel to get the tunnel's encap. Add an encap arg to
l2tp_session_set_header_len to avoid using session->tunnel.
If l2tpv3 sessions have colliding IDs, it is possible for
l2tp_v3_session_get to race with l2tp_session_register and fetch a
session which doesn't yet have session->tunnel set. Add a check for
this case.
Severity
7.8 (High)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-10-22 13:37 UTC
Assigner
References
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
3953ae7b218df4d1e544b98a393666f9ae58a78c , < f7415e60c25a6108cd7955a20b2e66b6251ffe02
(git)
Affected: 3953ae7b218df4d1e544b98a393666f9ae58a78c , < 24256415d18695b46da06c93135f5b51c548b950 (git) Affected: b102bfc2a90d14f342580285782a9a51c74f7369 (git) Affected: 10c15ddabbcf888922adbdd44ca3fecf6eab19d9 (git) Affected: 8d1c650d452c53fcb3f02a7b1d772741639f89a4 (git) Affected: 12b5fb58ac993c24210cf8cbc72d407d3a4e6490 (git) Affected: aef37401b467a0b1a9517c69924a1d66937e0789 (git) Affected: 3.2.99 , < 3.3 (semver) Affected: 3.16.54 , < 3.17 (semver) Affected: 4.4.225 , < 4.5 (semver) Affected: 4.9.225 , < 4.10 (semver) Affected: 4.14.182 , < 4.15 (semver) |
guessed | |
| Linux | Linux |
Affected:
4.15
Unaffected: 0 , < 4.15 (semver) Unaffected: 6.11.3 , ≤ 6.11.* (semver) Unaffected: 6.12 , ≤ * (original_commit_for_fix) |
guessed |
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"status": "final",
"title": "kernel: l2tp: prevent possible tunnel refcount underflow",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2024/cve-2024-49940.json",
"version": "3"
},
"vulnrichment": {
"containers": {
"adp": [
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"metrics": [
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"other": {
"content": {
"id": "CVE-2024-49940",
"options": [
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"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2024-10-22T13:37:52.827630Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2024-10-22T13:37:56.128Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
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],
"cna": {
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"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"net/l2tp/l2tp_core.c",
"net/l2tp/l2tp_core.h",
"net/l2tp/l2tp_netlink.c",
"net/l2tp/l2tp_ppp.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
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"lessThan": "f7415e60c25a6108cd7955a20b2e66b6251ffe02",
"status": "affected",
"version": "3953ae7b218df4d1e544b98a393666f9ae58a78c",
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{
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"versionType": "git"
},
{
"status": "affected",
"version": "b102bfc2a90d14f342580285782a9a51c74f7369",
"versionType": "git"
},
{
"status": "affected",
"version": "10c15ddabbcf888922adbdd44ca3fecf6eab19d9",
"versionType": "git"
},
{
"status": "affected",
"version": "8d1c650d452c53fcb3f02a7b1d772741639f89a4",
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},
{
"status": "affected",
"version": "12b5fb58ac993c24210cf8cbc72d407d3a4e6490",
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{
"status": "affected",
"version": "aef37401b467a0b1a9517c69924a1d66937e0789",
"versionType": "git"
},
{
"lessThan": "3.3",
"status": "affected",
"version": "3.2.99",
"versionType": "semver"
},
{
"lessThan": "3.17",
"status": "affected",
"version": "3.16.54",
"versionType": "semver"
},
{
"lessThan": "4.5",
"status": "affected",
"version": "4.4.225",
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},
{
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}
]
},
{
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"programFiles": [
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"net/l2tp/l2tp_core.h",
"net/l2tp/l2tp_netlink.c",
"net/l2tp/l2tp_ppp.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "4.15"
},
{
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"status": "unaffected",
"version": "0",
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},
{
"lessThanOrEqual": "6.11.*",
"status": "unaffected",
"version": "6.11.3",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "6.12",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
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"versionEndExcluding": "6.11.3",
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"vulnerable": true
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{
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},
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{
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}
],
"negate": false,
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}
],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nl2tp: prevent possible tunnel refcount underflow\n\nWhen a session is created, it sets a backpointer to its tunnel. When\nthe session refcount drops to 0, l2tp_session_free drops the tunnel\nrefcount if session-\u003etunnel is non-NULL. However, session-\u003etunnel is\nset in l2tp_session_create, before the tunnel refcount is incremented\nby l2tp_session_register, which leaves a small window where\nsession-\u003etunnel is non-NULL when the tunnel refcount hasn\u0027t been\nbumped.\n\nMoving the assignment to l2tp_session_register is trivial but\nl2tp_session_create calls l2tp_session_set_header_len which uses\nsession-\u003etunnel to get the tunnel\u0027s encap. Add an encap arg to\nl2tp_session_set_header_len to avoid using session-\u003etunnel.\n\nIf l2tpv3 sessions have colliding IDs, it is possible for\nl2tp_v3_session_get to race with l2tp_session_register and fetch a\nsession which doesn\u0027t yet have session-\u003etunnel set. Add a check for\nthis case."
}
],
"providerMetadata": {
"dateUpdated": "2026-05-23T15:54:05.584Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/f7415e60c25a6108cd7955a20b2e66b6251ffe02"
},
{
"url": "https://git.kernel.org/stable/c/24256415d18695b46da06c93135f5b51c548b950"
}
],
"title": "l2tp: prevent possible tunnel refcount underflow",
"x_generator": {
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}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2024-49940",
"datePublished": "2024-10-21T18:01:59.668Z",
"dateReserved": "2024-10-21T12:17:06.043Z",
"dateUpdated": "2026-05-23T15:54:05.584Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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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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