CVE-2026-68398High· 7.8▾ MidnightPoC availableIn the Linux kernel, the following vulnerability has been resolved: ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF pppol2tp_recv() runs in the L2TP UDP-encap softirq RX path: l2tp_udp_encap_recv() -> l2tp_recv_…
▾ Midnight zone — Critical, or high with PoC / in-the-wild
impact 42.9 · likelihood 0 · exploitation 12
A public proof-of-concept already exists for this vulnerability — see Exploit availability below.
Public exploit / PoC code seen in 1 source. Availability, not in-the-wild use.
Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake. The CVSS score shown above comes from the assigning CNA record, not NVD.
Exploit-prediction probability, daily snapshots since Oct 16.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via CVEORG
0.2%
Last analysed / modified upstream
0.2% → 0.2%
1 GitHub repo (last check)
In the Linux kernel, the following vulnerability has been resolved:
ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF
pppol2tp_recv() runs in the L2TP UDP-encap softirq RX path:
l2tp_udp_encap_recv() -> l2tp_recv_common() -> pppol2tp_recv() -> ppp_input(&po->chan)
It runs under rcu_read_lock() holding only an l2tp_session reference and takes NO reference on the internal PPP channel (struct channel, chan->ppp) that ppp_input() dereferences.
The pppox socket is SOCK_RCU_FREE, so 'po' and the embedded ppp_channel are RCU-safe. But the internal struct channel is a separate allocation that ppp_release_channel() frees with a plain kfree():
close(data socket) -> pppol2tp_release() -> pppox_unbind_sock() -> ppp_unregister_channel() -> ppp_release_channel() -> kfree(pch)
For a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit (no PPPIOCCONNECT, pch->ppp == NULL) and not bridged, teardown skips both ppp_disconnect_channel()'s synchronize_net() and ppp_unbridge_channels()'s synchronize_rcu(), so the kfree() has no grace period. rcu_read_lock() in pppol2tp_recv() does not protect against a plain kfree(), so an in-flight ppp_input() on one CPU can dereference the channel just freed by close() on another CPU.
The bug is reachable by an unprivileged user.
Defer the channel free to an RCU callback via call_rcu() so the grace period fences any in-flight ppp_input(). The disconnect and unbridge teardown paths already fence with synchronize_net()/synchronize_rcu(); call_rcu() does the same here without stalling the close() path.
Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 4e47f1ac188ece11d6fdabe44166a2776cc5bd4eLinux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 110b765744b147c63882f5e9cb12931c5dc8d85fLinux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 4bb84e964ff0fe0a171c965362de72f9820dbce9Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 3ab32218d7182705dae5c86f13925f458072da2cLinux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < c9574b8a8edeb4edd3ac6472c27ef7184bdb2baaLinux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < 06213c85d8c0994f786c093b8b2a517987943ca6Linux >= ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 < ec4215683e47424c9c4762fd3c60f552a3119142Linux d36e5ba7bbed5d7bd26e8609ffed503c2def401bLinux 9bcc0508576b2d50efd958f2ea1c5906749c2c89Linux c2984681fe15cfb803a9132aaaf1140ab20a72c1Linux 5803ecd7f6ac6f747582e775caa62ac9d0489261Linux 26f8819ddd10141ebe7bbce700fbab36bfa5f478Linux >= 3.2.99 < 3.3Linux >= 3.16.54 < 3.17Linux >= 4.4.225 < 4.5Linux >= 4.9.225 < 4.10Linux >= 4.14.182 < 4.15Linux 4.15Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Connected by shared product, vendor, weakness, or advisory.
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