CVE-2024-49940
- Source
- https://nvd.nist.gov/vuln/detail/CVE-2024-49940
- Import Source
- https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2024-49940.json
- JSON Data
- https://api.test.osv.dev/v1/vulns/CVE-2024-49940
- Downstream
- Related
- Published
- 2024-10-21T18:15:15Z
- Modified
- 2025-08-09T20:01:28Z
- Severity
-
- 5.5 (Medium) CVSS_V3 - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H CVSS Calculator
- Summary
- [none]
- Details
-
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, l2tpsessionfree drops the tunnel refcount if session->tunnel is non-NULL. However, session->tunnel is set in l2tpsessioncreate, before the tunnel refcount is incremented by l2tpsessionregister, which leaves a small window where session->tunnel is non-NULL when the tunnel refcount hasn't been bumped.
Moving the assignment to l2tpsessionregister is trivial but l2tpsessioncreate calls l2tpsessionsetheaderlen which uses session->tunnel to get the tunnel's encap. Add an encap arg to l2tpsessionsetheaderlen to avoid using session->tunnel.
If l2tpv3 sessions have colliding IDs, it is possible for l2tpv3sessionget to race with l2tpsession_register and fetch a session which doesn't yet have session->tunnel set. Add a check for this case.
- References