# CVE-2024-49940: l2tp: prevent possible tunnel refcount underflow CVE-2024-49940 is fixed in 26 products on 1 platform, first by DEBIAN-CVE-2024-49940, released October 21, 2024. It is not reported as exploited. Patch Radar priority: Routine. - Web page: https://patchblox.com/security/cve/CVE-2024-49940 - Priority: Routine - CVSS: 5.5 (medium) - EPSS: 0.0033 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Oct 21, 2024 - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2024-49940 ## Description 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. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | dtb-aarch64 opensuse-leap 15.6 | 6.4.0-150600.23.47.1 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-64kb opensuse-leap 15.6 | 6.4.0-150600.23.47.2 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-64kb sles 15.6 | 6.4.0-150600.23.47.2 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-azure opensuse-leap 15.6 | 6.4.0-150600.8.34.2 | [SUSE-SU-2025:1177-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1177-1.md) | Apr 8, 2025 | | Linux | kernel-azure sles 15.6 | 6.4.0-150600.8.34.2 | [SUSE-SU-2025:1177-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1177-1.md) | Apr 8, 2025 | | Linux | kernel-coco sles 15.6 | 6.4.0-15061.21.coco15sp6.1 | [SUSE-SU-2025:01919-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-01919-1.md) | Jun 12, 2025 | | Linux | kernel-coco_debug sles 15.6 | 6.4.0-15061.21.coco15sp6.1 | [SUSE-SU-2025:01919-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-01919-1.md) | Jun 12, 2025 | | Linux | kernel-debug opensuse-leap 15.6 | 6.4.0-150600.23.47.2 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-default opensuse-leap 15.6 | 6.4.0-150600.23.47.2 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-default sles 15.6 | 6.4.0-150600.23.47.2 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-default-base opensuse-leap 15.6 | 6.4.0-150600.23.47.2.150600.12.20.2 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-default-base sles 15.6 | 6.4.0-150600.23.47.2.150600.12.20.2 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-docs opensuse-leap 15.6 | 6.4.0-150600.23.47.1 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-docs sles 15.6 | 6.4.0-150600.23.47.1 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-kvmsmall opensuse-leap 15.6 | 6.4.0-150600.23.47.2 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-livepatch-SLE15-SP6-RT_Update_10 sles 15.6 | 1-150600.1.5.1 | [SUSE-SU-2025:1178-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1178-1.md) | Apr 8, 2025 | | Linux | kernel-livepatch-SLE15-SP6_Update_10 sles 15.6 | 1-150600.13.5.1 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-obs-build opensuse-leap 15.6 | 6.4.0-150600.23.47.1 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-obs-build sles 15.6 | 6.4.0-150600.23.47.1 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-obs-qa opensuse-leap 15.6 | 6.4.0-150600.23.47.1 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-rt opensuse-leap 15.6 | 6.4.0-150600.10.34.1 | [SUSE-SU-2025:1178-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1178-1.md) | Apr 8, 2025 | | Linux | kernel-rt_debug opensuse-leap 15.6 | 6.4.0-150600.10.34.1 | [SUSE-SU-2025:1178-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1178-1.md) | Apr 8, 2025 | | Linux | kernel-source opensuse-leap 15.6 | 6.4.0-150600.23.47.2 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-source sles 15.6 | 6.4.0-150600.23.47.2 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-source-azure opensuse-leap 15.6 | 6.4.0-150600.8.34.2 | [SUSE-SU-2025:1177-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1177-1.md) | Apr 8, 2025 | | Linux | kernel-source-azure sles 15.6 | 6.4.0-150600.8.34.2 | [SUSE-SU-2025:1177-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1177-1.md) | Apr 8, 2025 | | Linux | kernel-source-coco sles 15.6 | 6.4.0-15061.21.coco15sp6.1 | [SUSE-SU-2025:01919-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-01919-1.md) | Jun 12, 2025 | | Linux | kernel-source-rt opensuse-leap 15.6 | 6.4.0-150600.10.34.1 | [SUSE-SU-2025:1178-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1178-1.md) | Apr 8, 2025 | | Linux | kernel-syms opensuse-leap 15.6 | 6.4.0-150600.23.47.1 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-syms sles 15.6 | 6.4.0-150600.23.47.1 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-syms-azure opensuse-leap 15.6 | 6.4.0-150600.8.34.1 | [SUSE-SU-2025:1177-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1177-1.md) | Apr 8, 2025 | | Linux | kernel-syms-azure sles 15.6 | 6.4.0-150600.8.34.1 | [SUSE-SU-2025:1177-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1177-1.md) | Apr 8, 2025 | | Linux | kernel-syms-coco sles 15.6 | 6.4.0-15061.21.coco15sp6.1 | [SUSE-SU-2025:01919-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-01919-1.md) | Jun 12, 2025 | | Linux | kernel-syms-rt opensuse-leap 15.6 | 6.4.0-150600.10.34.1 | [SUSE-SU-2025:1178-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1178-1.md) | Apr 8, 2025 | | Linux | kernel-zfcpdump opensuse-leap 15.6 | 6.4.0-150600.23.47.2 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | kernel-zfcpdump sles 15.6 | 6.4.0-150600.23.47.2 | [SUSE-SU-2025:1180-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-1180-1.md) | Apr 9, 2025 | | Linux | linux Debian 13.5 (trixie) | 6.11.4-1 | [DEBIAN-CVE-2024-49940](https://patchblox.com/security/data/fix/linux/debian-cve-2024-49940.md) | Oct 21, 2024 | | Linux | linux Debian 14 | 6.11.4-1 | [DEBIAN-CVE-2024-49940](https://patchblox.com/security/data/fix/linux/debian-cve-2024-49940.md) | Oct 21, 2024 | --- Data as of 2026-11-08T13:06:02Z UTC. 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