TI-2024-33391 Aliases CVE-2024-49940 GHSA-h9jc-p2cr-c4rx

l2tp: prevent possible tunnel refcount underflow

LOW 34Published 2024-10-21 · Updated 2026-10-30

Key facts

Attack vector: Local
Privileges required: Low
User interaction: None
Attack complexity: Low
Impact type: —
Confidentiality · integrity · availability: High · High · High
Fix status: Partial Red Hat: 3 without a fix

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat.

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00325 25th percentileScored 2026-11-07

Fix Partial Linux (Linux): 3.3, 3.17, 4.5 +6Red Hat: 3 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
Linux	Linux	3.2.99 to before 3.3; 3.16.54 to before 3.17; 4.4.225 to before 4.5; 4.9.225 to before 4.10; 4.14.182 to before 4.15	3.3, 3.17, 4.5, 4.10, 4.15	Patch available	CNA
Linux	Linux	4.15 and later	6.1.191, 6.6.160, 6.11.3, 6.12	Patch available	CNA

Linux VendorLinux Affected 3.2.99 to before 3.3; 3.16.54 to before 3.17; 4.4.225 to before 4.5; 4.9.225 to before 4.10; 4.14.182 to before 4.15 Fixed in 3.3, 3.17, 4.5, 4.10, 4.15 Patch available CNA
Linux VendorLinux Affected 4.15 and later Fixed in 6.1.191, 6.6.160, 6.11.3, 6.12 Patch available CNA

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:o:linux:linux_kernel::::::::	before 6.11.3	Vulnerable	Linux

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* Versions before 6.11.3 Vulnerable ·Linux

Remediation

Fix · CNA Linux (Linux) Fixed in 3.3, 3.17, 4.5, 4.10, 4.15
Fix · CNA Linux (Linux) Fixed in 6.1.191, 6.6.160, 6.11.3, 6.12

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

Product	Status	Plan or fix
Red Hat Enterprise Linux 7	Affected	No fix planned: Out of support scope
Red Hat Enterprise Linux 8	Affected	No fix planned: Will not fix
Red Hat Enterprise Linux 9	Affected	No fix planned: Will not fix

Not affected: 1 product

Red Hat Enterprise Linux 6

Timeline

2026-10-02 Threatist record created from CVE-2024-49940
2026-10-03 Alias added: GHSA-h9jc-p2cr-c4rx
2026-10-21 Fix available: Linux/[email protected], Linux/Linux@98691b2e28a6c3dac0680914493d54c77f215755 · CNA
2026-10-21 1 new reference · CNA
2026-10-30 Fix available: Linux/[email protected], Linux/Linux@aa7132362e79abc4f2add4d8657dd1679341edc5 · CNA
2026-10-30 1 new reference · CNA

References

Patch 2

Other 2

TI-2025-26358 tls: fix handling of zero-length records on the rx_list KEVCVSS 3.1CRITICAL 9.8
TI-2026-38352 netfilter: bridge: make ebt_snat ARP rewrite writable KEVCVSS 3.1HIGH 8.8
TI-2013-05264 The (1) get_user and (2) put_user API functions in the Linux kernel before 3.5.5 on the… KEVCVSS 3.1HIGH 8.8
TI-2022-00125 Integer overflow in kernel KEVCVSS 3.1HIGH 8.4
TI-2013-01864 The perf_swevent_init function in kernel/events/core.c in the Linux kernel before 3.8.9… KEVCVSS 3.1HIGH 8.4
TI-2021-05514 Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACE KEVCVSS 3.1HIGH 8.3

See all 15278 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences