CVE-2026-68398 is a vulnerability in Linux Kernel
Published on August 10, 2026
ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF
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.
Products Associated with CVE-2026-68398
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Affected Versions
Linux:- Version ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 and below 4bb84e964ff0fe0a171c965362de72f9820dbce9 is affected.
- Version ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 and below 3ab32218d7182705dae5c86f13925f458072da2c is affected.
- Version ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 and below c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa is affected.
- Version ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 and below 06213c85d8c0994f786c093b8b2a517987943ca6 is affected.
- Version ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 and below ec4215683e47424c9c4762fd3c60f552a3119142 is affected.
- Version d36e5ba7bbed5d7bd26e8609ffed503c2def401b is affected.
- Version 9bcc0508576b2d50efd958f2ea1c5906749c2c89 is affected.
- Version c2984681fe15cfb803a9132aaaf1140ab20a72c1 is affected.
- Version 5803ecd7f6ac6f747582e775caa62ac9d0489261 is affected.
- Version 26f8819ddd10141ebe7bbce700fbab36bfa5f478 is affected.
- Version 3.2.99 and below 3.3 is affected.
- Version 3.16.54 and below 3.17 is affected.
- Version 4.4.225 and below 4.5 is affected.
- Version 4.9.225 and below 4.10 is affected.
- Version 4.14.182 and below 4.15 is affected.
- Version 4.15 is affected.
- Before 4.15 is unaffected.
- Version 6.6.148, <= 6.6.* is unaffected.
- Version 6.12.101, <= 6.12.* is unaffected.
- Version 6.18.42, <= 6.18.* is unaffected.
- Version 7.1.6, <= 7.1.* is unaffected.
- Version 7.2-rc4, <= * is unaffected.