{"cve":"CVE-2026-68398","nvd":{"published":"2026-08-10T13:20:33.243","modified":"2026-10-19T22:17:17.243","status":"Received","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF\n\npppol2tp_recv() runs in the L2TP UDP-encap softirq RX path:\n\n l2tp_udp_encap_recv() -> l2tp_recv_common() -> pppol2tp_recv()\n   -> ppp_input(&po->chan)\n\nIt runs under rcu_read_lock() holding only an l2tp_session reference and\ntakes NO reference on the internal PPP channel (struct channel,\nchan->ppp) that ppp_input() dereferences.\n\nThe pppox socket is SOCK_RCU_FREE, so 'po' and the embedded ppp_channel\nare RCU-safe.  But the internal struct channel is a separate allocation\nthat ppp_release_channel() frees with a plain kfree():\n\n close(data socket) -> pppol2tp_release() -> pppox_unbind_sock()\n   -> ppp_unregister_channel() -> ppp_release_channel() -> kfree(pch)\n\nFor a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit\n(no PPPIOCCONNECT, pch->ppp == NULL) and not bridged, teardown skips\nboth ppp_disconnect_channel()'s synchronize_net() and\nppp_unbridge_channels()'s synchronize_rcu(), so the kfree() has no grace\nperiod.  rcu_read_lock() in pppol2tp_recv() does not protect against a\nplain kfree(), so an in-flight ppp_input() on one CPU can dereference\nthe channel just freed by close() on another CPU.\n\nThe bug is reachable by an unprivileged user.\n\nDefer the channel free to an RCU callback via call_rcu() so the grace\nperiod fences any in-flight ppp_input(). The disconnect and unbridge\nteardown paths already fence with synchronize_net()/synchronize_rcu();\ncall_rcu() does the same here without stalling the close() path.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.8},"cwes":["CWE-416"],"references":["https://git.kernel.org/stable/c/06213c85d8c0994f786c093b8b2a517987943ca6","https://git.kernel.org/stable/c/110b765744b147c63882f5e9cb12931c5dc8d85f","https://git.kernel.org/stable/c/3ab32218d7182705dae5c86f13925f458072da2c","https://git.kernel.org/stable/c/4bb84e964ff0fe0a171c965362de72f9820dbce9","https://git.kernel.org/stable/c/4e47f1ac188ece11d6fdabe44166a2776cc5bd4e"],"products":[],"source":"nvd","synced_at":"2026-10-21T03:56:58.798400159+00:00"},"epss":{"cve":"CVE-2026-68398","score":0.00232,"percentile":0.13992,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}