Linux: Use After Free
CVE-2026-23209 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 da5c6b8ae47e414be47e5e04def15b25d5c962dc, 5dae6b36a7cb7a4fcf4121b95e9ca7f96f816c8a, c43d0e787cbba569ec9d11579ed370b50fab6c9c 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 0.17% 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 da5c6b8ae47e414be47e5e04def15b25d5c962dc or 5dae6b36a7cb7a4fcf4121b95e9ca7f96f816c8a or c43d0e787cbba569ec9d11579ed370b50fab6c9c or 11ba9f0dc865136174cb98834280fb21bbc950c7, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.10.250 or 5.15.200 or 6.1.163 or 6.6.124, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | aa5fd0fb77486b8a6764ead8627baa14790e4280 up to, but not including, da5c6b8ae47e414be47e5e04def15b25d5c962dc; aa5fd0fb77486b8a6764ead8627baa14790e4280 up to, but not including, 5dae6b36a7cb7a4fcf4121b95e9ca7f96f816c8a; aa5fd0fb77486b8a6764ead8627baa14790e4280 up to, but not including, c43d0e787cbba569ec9d11579ed370b50fab6c9c; aa5fd0fb77486b8a6764ead8627baa14790e4280 up to, but not including, 11ba9f0dc865136174cb98834280fb21bbc950c7; aa5fd0fb77486b8a6764ead8627baa14790e4280 up to, but not including, 986967a162142710076782d5b93daab93a892980; aa5fd0fb77486b8a6764ead8627baa14790e4280 up to, but not including, cdedcd5aa3f3cb8b7ae0f87ab3a936d0bd583d66; aa5fd0fb77486b8a6764ead8627baa14790e4280 up to, but not including, f8db6475a83649689c087a8f52486fcc53e627e9; 4.9 | da5c6b8ae47e414be47e5e04def15b25d5c962dc, 5dae6b36a7cb7a4fcf4121b95e9ca7f96f816c8a, c43d0e787cbba569ec9d11579ed370b50fab6c9c, 11ba9f0dc865136174cb98834280fb21bbc950c7, 986967a162142710076782d5b93daab93a892980, cdedcd5aa3f3cb8b7ae0f87ab3a936d0bd583d66 |
| Linux | Linux Kernel | 4.9.1 up to, but not including, 5.10.250; 5.11 up to, but not including, 5.15.200; 5.16 up to, but not including, 6.1.163; 6.2 up to, but not including, 6.6.124; 6.7 up to, but not including, 6.12.70; 6.13 up to, but not including, 6.18.10; 4.9; 6.19 | 5.10.250, 5.15.200, 6.1.163, 6.6.124, 6.12.70, 6.18.10 |
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 NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA |
| CVSS 3.1 | 7.8 | High | NVD |
Official description
In the Linux kernel, the following vulnerability has been resolved: macvlan: fix error recovery in macvlan_common_newlink() valis provided a nice repro to crash the kernel: ip link add p1 type veth peer p2 ip link set address 00:00:00:00:00:20 dev p1 ip link set up dev p1 ip link set up dev p2 ip link add mv0 link p2 type macvlan mode source ip link add invalid% link p2 type macvlan mode source macaddr add 00:00:00:00:00:20 ping -c1 -I p1 1.2.3.4 He also gave a very detailed analysis: <quote valis> The issue is triggered when a new macvlan link is created with MACVLAN_MODE_SOURCE mode and MACVLAN_MACADDR_ADD (or MACVLAN_MACADDR_SET) parameter, lower device already has a macvlan port and register_netdevice() called from macvlan_common_newlink() fails (e.g. because of the invalid link name). In this case macvlan_hash_add_source is called from macvlan_change_sources() / macvlan_common_newlink(): This adds a reference to vlan to the port's vlan_source_hash using macvlan_source_entry. vlan is a pointer to the priv data of the link that is being created. When register_netdevice() fails, the error is returned from macvlan_newlink() to rtnl_newlink_create(): if (ops->newlink) err = ops->newlink(dev, ¶ms, extack); else err = register_netdevice(dev); if (err < 0) { free_netdev(dev); goto out; } and free_netdev() is called, causing a kvfree() on the struct net_device that is still referenced in the source entry attached to the lower device's macvlan port. Now all packets sent on the macvlan port with a matching source mac address will trigger a use-after-free in macvlan_forward_source(). </quote valis> With all that, my fix is to make sure we call macvlan_flush_sources() regardless of @create value whenever "goto destroy_macvlan_port;" path is taken. Many thanks to valis for following up on this issue.
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/11ba9f0dc865136174cb98834280fb21bbc950c7
- git.kernel.org/stable/c/5dae6b36a7cb7a4fcf4121b95e9ca7f96f816c8a
- git.kernel.org/stable/c/986967a162142710076782d5b93daab93a892980
- git.kernel.org/stable/c/c43d0e787cbba569ec9d11579ed370b50fab6c9c
- git.kernel.org/stable/c/cdedcd5aa3f3cb8b7ae0f87ab3a936d0bd583d66
- git.kernel.org/stable/c/da5c6b8ae47e414be47e5e04def15b25d5c962dc
- git.kernel.org/stable/c/f8db6475a83649689c087a8f52486fcc53e627e9
Recent Use After Free vulnerabilities
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.0 High severity
- 7.8 High severity
- 7.8 High severity
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