{"id":"CVE-2026-68398","title":"ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF","summary":"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_…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 4e47f1ac188ece11d6fdabe44166a2776cc5bd4e","Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 110b765744b147c63882f5e9cb12931c5dc8d85f","Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 4bb84e964ff0fe0a171c965362de72f9820dbce9","Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 3ab32218d7182705dae5c86f13925f458072da2c","Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa","Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 06213c85d8c0994f786c093b8b2a517987943ca6","Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < ec4215683e47424c9c4762fd3c60f552a3119142","Linux d36e5ba7bbed5d7bd26e8609ffed503c2def401b","Linux 9bcc0508576b2d50efd958f2ea1c5906749c2c89","Linux c2984681fe15cfb803a9132aaaf1140ab20a72c1","Linux 5803ecd7f6ac6f747582e775caa62ac9d0489261","Linux 26f8819ddd10141ebe7bbce700fbab36bfa5f478","Linux >= 3.2.99 < 3.3","Linux >= 3.16.54 < 3.17","Linux >= 4.4.225 < 4.5","Linux >= 4.9.225 < 4.10","Linux >= 4.14.182 < 4.15","Linux 4.15"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-10-16T15:48:09.975001Z"},"exploitAvailable":true,"published":"2026-08-10","updated":"2026-10-16","sourceUpdated":"2026-10-16T15:53:11.735Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-68398","references":[{"url":"https://git.kernel.org/stable/c/4e47f1ac188ece11d6fdabe44166a2776cc5bd4e"},{"url":"https://git.kernel.org/stable/c/110b765744b147c63882f5e9cb12931c5dc8d85f"},{"url":"https://git.kernel.org/stable/c/4bb84e964ff0fe0a171c965362de72f9820dbce9"},{"url":"https://git.kernel.org/stable/c/3ab32218d7182705dae5c86f13925f458072da2c"},{"url":"https://git.kernel.org/stable/c/c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa"},{"url":"https://git.kernel.org/stable/c/06213c85d8c0994f786c093b8b2a517987943ca6"},{"url":"https://git.kernel.org/stable/c/ec4215683e47424c9c4762fd3c60f552a3119142"}],"tags":["cve.org","exploit-available"],"epss":0.00195,"epssPercentile":0.086,"exploits":{"github":1,"githubRepos":["https://github.com/aramosf/CVE-2026-68398"],"checkedAt":"2026-10-16T17:25:21.017Z"},"ingestedAt":"2026-10-16T17:24:46.865Z","slug":"CVE-2026-68398","body":"## Overview\n\nIn 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.\n\n## Affected\n\n- `Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 4e47f1ac188ece11d6fdabe44166a2776cc5bd4e`\n- `Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 110b765744b147c63882f5e9cb12931c5dc8d85f`\n- `Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 4bb84e964ff0fe0a171c965362de72f9820dbce9`\n- `Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 3ab32218d7182705dae5c86f13925f458072da2c`\n- `Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa`\n- `Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 06213c85d8c0994f786c093b8b2a517987943ca6`\n- `Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < ec4215683e47424c9c4762fd3c60f552a3119142`\n- `Linux d36e5ba7bbed5d7bd26e8609ffed503c2def401b`\n- `Linux 9bcc0508576b2d50efd958f2ea1c5906749c2c89`\n- `Linux c2984681fe15cfb803a9132aaaf1140ab20a72c1`\n- `Linux 5803ecd7f6ac6f747582e775caa62ac9d0489261`\n- `Linux 26f8819ddd10141ebe7bbce700fbab36bfa5f478`\n- `Linux >= 3.2.99 < 3.3`\n- `Linux >= 3.16.54 < 3.17`\n- `Linux >= 4.4.225 < 4.5`\n- `Linux >= 4.9.225 < 4.10`\n- `Linux >= 4.14.182 < 4.15`\n- `Linux 4.15`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":55,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":12,"ransomware":0},"changes":[]}