l2tp: prevent possible tunnel refcount underflow

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2024-49940
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2024-10-21 18:15:15 UTC
Updated2026-10-21 13:17:49 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.002220000 probability, percentile 0.127650000 (date 2026-08-06)

Problem Types: NVD-CWE-noinfo

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary5.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 3953ae7b218df4d1e544b98a393666f9ae58a78c 98691b2e28a6c3dac0680914493d54c77f215755 git Not specified
CNA Linux Linux affected 3953ae7b218df4d1e544b98a393666f9ae58a78c f7415e60c25a6108cd7955a20b2e66b6251ffe02 git Not specified
CNA Linux Linux affected 3953ae7b218df4d1e544b98a393666f9ae58a78c 24256415d18695b46da06c93135f5b51c548b950 git Not specified
CNA Linux Linux affected b102bfc2a90d14f342580285782a9a51c74f7369 git Not specified
CNA Linux Linux affected 10c15ddabbcf888922adbdd44ca3fecf6eab19d9 git Not specified
CNA Linux Linux affected 8d1c650d452c53fcb3f02a7b1d772741639f89a4 git Not specified
CNA Linux Linux affected 12b5fb58ac993c24210cf8cbc72d407d3a4e6490 git Not specified
CNA Linux Linux affected aef37401b467a0b1a9517c69924a1d66937e0789 git Not specified
CNA Linux Linux affected 3.2.99 3.3 semver Not specified
CNA Linux Linux affected 3.16.54 3.17 semver Not specified
CNA Linux Linux affected 4.4.225 4.5 semver Not specified
CNA Linux Linux affected 4.9.225 4.10 semver Not specified
CNA Linux Linux affected 4.14.182 4.15 semver Not specified
CNA Linux Linux affected 4.15 Not specified
CNA Linux Linux unaffected 4.15 semver Not specified
CNA Linux Linux unaffected 6.6.160 6.6.* semver Not specified
CNA Linux Linux unaffected 6.11.3 6.11.* semver Not specified
CNA Linux Linux unaffected 6.12 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/24256415d18695b46da06c93135f5b51c548b950 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/f7415e60c25a6108cd7955a20b2e66b6251ffe02 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/98691b2e28a6c3dac0680914493d54c77f215755 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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