CVE-2026-68398
ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF
Description
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.
INFO
Published Date :
Aug. 10, 2026, 1:20 p.m.
Last Modified :
Aug. 10, 2026, 1:20 p.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Affected Products
The following products are affected by CVE-2026-68398
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
Solution
- Update the Linux kernel.
- Defer channel free to an RCU callback via call_rcu().
- Ensure teardown paths fence properly.
- Avoid plain kfree() without a grace period.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-68398.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-68398 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-68398
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-68398 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-68398 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Aug. 10, 2026
Action Type Old Value New Value Added Affected [{'repo': 'https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git', 'vendor': 'Linux', 'product': 'Linux', 'versions': [{'status': 'affected', 'version': 'ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741', 'lessThan': '4bb84e964ff0fe0a171c965362de72f9820dbce9', 'versionType': 'git'}, {'status': 'affected', 'version': 'ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741', 'lessThan': '3ab32218d7182705dae5c86f13925f458072da2c', 'versionType': 'git'}, {'status': 'affected', 'version': 'ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741', 'lessThan': 'c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa', 'versionType': 'git'}, {'status': 'affected', 'version': 'ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741', 'lessThan': '06213c85d8c0994f786c093b8b2a517987943ca6', 'versionType': 'git'}, {'status': 'affected', 'version': 'ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741', 'lessThan': 'ec4215683e47424c9c4762fd3c60f552a3119142', 'versionType': 'git'}, {'status': 'affected', 'version': 'd36e5ba7bbed5d7bd26e8609ffed503c2def401b', 'versionType': 'git'}, {'status': 'affected', 'version': '9bcc0508576b2d50efd958f2ea1c5906749c2c89', 'versionType': 'git'}, {'status': 'affected', 'version': 'c2984681fe15cfb803a9132aaaf1140ab20a72c1', 'versionType': 'git'}, {'status': 'affected', 'version': '5803ecd7f6ac6f747582e775caa62ac9d0489261', 'versionType': 'git'}, {'status': 'affected', 'version': '26f8819ddd10141ebe7bbce700fbab36bfa5f478', 'versionType': 'git'}, {'status': 'affected', 'version': '3.2.99', 'lessThan': '3.3', 'versionType': 'semver'}, {'status': 'affected', 'version': '3.16.54', 'lessThan': '3.17', 'versionType': 'semver'}, {'status': 'affected', 'version': '4.4.225', 'lessThan': '4.5', 'versionType': 'semver'}, {'status': 'affected', 'version': '4.9.225', 'lessThan': '4.10', 'versionType': 'semver'}, {'status': 'affected', 'version': '4.14.182', 'lessThan': '4.15', 'versionType': 'semver'}], 'programFiles': ['drivers/net/ppp/ppp_generic.c'], 'defaultStatus': 'unaffected'}, {'repo': 'https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git', 'vendor': 'Linux', 'product': 'Linux', 'versions': [{'status': 'affected', 'version': '4.15'}, {'status': 'unaffected', 'version': '0', 'lessThan': '4.15', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '6.6.148', 'versionType': 'semver', 'lessThanOrEqual': '6.6.*'}, {'status': 'unaffected', 'version': '6.12.101', 'versionType': 'semver', 'lessThanOrEqual': '6.12.*'}, {'status': 'unaffected', 'version': '6.18.42', 'versionType': 'semver', 'lessThanOrEqual': '6.18.*'}, {'status': 'unaffected', 'version': '7.1.6', 'versionType': 'semver', 'lessThanOrEqual': '7.1.*'}, {'status': 'unaffected', 'version': '7.2-rc4', 'versionType': 'original_commit_for_fix', 'lessThanOrEqual': '*'}], 'programFiles': ['drivers/net/ppp/ppp_generic.c'], 'defaultStatus': 'affected'}] Added Description 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. Added Reference https://git.kernel.org/stable/c/06213c85d8c0994f786c093b8b2a517987943ca6 Added Reference https://git.kernel.org/stable/c/3ab32218d7182705dae5c86f13925f458072da2c Added Reference https://git.kernel.org/stable/c/4bb84e964ff0fe0a171c965362de72f9820dbce9 Added Reference https://git.kernel.org/stable/c/c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa Added Reference https://git.kernel.org/stable/c/ec4215683e47424c9c4762fd3c60f552a3119142