Linux: Use After Free
CVE-2026-63803 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 86d80a231bde4cfb64bfbfbfffd83056fc93628f, 8308122bc9c065b1f376e081ed300129a2ac9545, ce8f9ddca0c9f217342a8b49efd309aa35b81a36 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 0.13% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to 86d80a231bde4cfb64bfbfbfffd83056fc93628f or 8308122bc9c065b1f376e081ed300129a2ac9545 or ce8f9ddca0c9f217342a8b49efd309aa35b81a36 or 508a0139d3bf60f6a03d2fbfb63a89a9463d983a, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.10.261 or 5.15.211 or 6.1.177 or 6.6.144, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, 86d80a231bde4cfb64bfbfbfffd83056fc93628f; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, 8308122bc9c065b1f376e081ed300129a2ac9545; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, ce8f9ddca0c9f217342a8b49efd309aa35b81a36; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, 508a0139d3bf60f6a03d2fbfb63a89a9463d983a; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, c64dbef1c0fbd36f9530aa75112acdf6a6d3cfd8; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, 5a84398101bf9f11e84b176343e4e3ba83e668c0; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, a594debfd4e7ec39413647458907f689ef57fd2f; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, c78a4e41ab5ead6193ad8a2dd92e8906bae659fa; and 1 more ranges | 86d80a231bde4cfb64bfbfbfffd83056fc93628f, 8308122bc9c065b1f376e081ed300129a2ac9545, ce8f9ddca0c9f217342a8b49efd309aa35b81a36, 508a0139d3bf60f6a03d2fbfb63a89a9463d983a, c64dbef1c0fbd36f9530aa75112acdf6a6d3cfd8, 5a84398101bf9f11e84b176343e4e3ba83e668c0 |
| Linux | Linux Kernel | 2.6.12.1 up to, but not including, 5.10.261; 5.11 up to, but not including, 5.15.211; 5.16 up to, but not including, 6.1.177; 6.2 up to, but not including, 6.6.144; 6.7 up to, but not including, 6.12.95; 6.13 up to, but not including, 6.18.38; 6.19 up to, but not including, 7.1.3; 2.6.12 | 5.10.261, 5.15.211, 6.1.177, 6.6.144, 6.12.95, 6.18.38 |
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: hdlc_ppp: sync per-proto timers before freeing hdlc state Each PPP control protocol (LCP/IPCP/IPV6CP) embedded in struct ppp registers a timer via timer_setup(). That struct ppp is the hdlc->state allocation, which detach_hdlc_protocol() frees with kfree() in both teardown paths: unregister_hdlc_device() and the re-attach inside attach_hdlc_protocol(). The ppp proto never registered a .detach callback, so detach_hdlc_protocol() performs no timer synchronization before the kfree(). The only cancel, timer_delete(&proto->timer) in ppp_cp_event(), is partial (it does not wait for a running callback) and only runs on the ->CLOSED transition; ppp_stop()/ppp_close() do not sync either. A ppp_timer callback already executing (blocked on ppp->lock) survives the kfree and then dereferences proto->state / ppp->lock in freed memory, leading to a use-after-free. Fix this by adding a .detach helper that calls timer_shutdown_sync() on every per-proto timer. detach_hdlc_protocol() invokes proto->detach(dev) before kfree(hdlc->state), so timer_shutdown_sync() now runs on both free paths. timer_shutdown_sync() is used instead of timer_delete_sync() because the keepalive path re-arms the timer through add_timer()/mod_timer() and shutdown blocks any re-activation during teardown. Initialize the per-protocol timers in ppp_ioctl() when the protocol is attached, and remove the now-redundant timer_setup() from ppp_start(), so that the timers are initialized exactly once at attach time and ppp_timer_release() never operates on uninitialized timer_list structures. attach_hdlc_protocol() uses kmalloc() (not kzalloc), so struct ppp's protos[i].timer is uninitialized garbage until the first timer_setup(); without this init-at-attach, attaching the PPP protocol without ever bringing the device up would leave timer_shutdown_sync() operating on uninitialized memory in .detach. Moving the init out of ppp_start() (which only runs on NETDEV_UP) into the attach path makes the initialization unconditional and avoids initializing the same timer_list twice. This bug was found by static analysis.
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.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/508a0139d3bf60f6a03d2fbfb63a89a9463d983a
- git.kernel.org/stable/c/5a84398101bf9f11e84b176343e4e3ba83e668c0
- git.kernel.org/stable/c/8308122bc9c065b1f376e081ed300129a2ac9545
- git.kernel.org/stable/c/86d80a231bde4cfb64bfbfbfffd83056fc93628f
- git.kernel.org/stable/c/a594debfd4e7ec39413647458907f689ef57fd2f
- git.kernel.org/stable/c/c64dbef1c0fbd36f9530aa75112acdf6a6d3cfd8
- git.kernel.org/stable/c/c78a4e41ab5ead6193ad8a2dd92e8906bae659fa
- git.kernel.org/stable/c/ce8f9ddca0c9f217342a8b49efd309aa35b81a36
Recent Use After Free vulnerabilities
- 8.8 High severity
- 9.8 Critical severity
- 9.8 Critical severity
- 7.8 High severity
- 9.8 Critical severity
- 8.8 High severity
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