CyberSecBulletin
CVE-2026-68398NVD status: Received

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2026-68398 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 4e47f1ac188ece11d6fdabe44166a2776cc5bd4e, 110b765744b147c63882f5e9cb12931c5dc8d85f, 4bb84e964ff0fe0a171c965362de72f9820dbce9 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.23% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to 4e47f1ac188ece11d6fdabe44166a2776cc5bd4e or 110b765744b147c63882f5e9cb12931c5dc8d85f or 4bb84e964ff0fe0a171c965362de72f9820dbce9 or 3ab32218d7182705dae5c86f13925f458072da2c, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 up to, but not including, 4e47f1ac188ece11d6fdabe44166a2776cc5bd4e; ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 up to, but not including, 110b765744b147c63882f5e9cb12931c5dc8d85f; ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 up to, but not including, 4bb84e964ff0fe0a171c965362de72f9820dbce9; ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 up to, but not including, 3ab32218d7182705dae5c86f13925f458072da2c; ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 up to, but not including, c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa; ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 up to, but not including, 06213c85d8c0994f786c093b8b2a517987943ca6; ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 up to, but not including, ec4215683e47424c9c4762fd3c60f552a3119142; d36e5ba7bbed5d7bd26e8609ffed503c2def401b; and 10 more ranges4e47f1ac188ece11d6fdabe44166a2776cc5bd4e, 110b765744b147c63882f5e9cb12931c5dc8d85f, 4bb84e964ff0fe0a171c965362de72f9820dbce9, 3ab32218d7182705dae5c86f13925f458072da2c, c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa, 06213c85d8c0994f786c093b8b2a517987943ca6

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.

Official 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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Use After Free

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.

How developers prevent this class of flaw

  • Choose a language that provides automatic memory management.
  • When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.

More Use After Free vulnerabilities (CWE-416)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Use After Free vulnerabilities

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