Linux: Use After Free
CVE-2026-23319 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 529e685e522b9d7fb379dbe6929dcdf520e34c8c, 9b02c5c4147f8af8ed783c8deb5df927a55c3951, cfcfa0ca0212162aa472551266038e8fd6768cff 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 0.14% 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 529e685e522b9d7fb379dbe6929dcdf520e34c8c or 9b02c5c4147f8af8ed783c8deb5df927a55c3951 or cfcfa0ca0212162aa472551266038e8fd6768cff or 3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.1.167 or 6.6.130 or 6.12.77 or 6.18.17, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e up to, but not including, 529e685e522b9d7fb379dbe6929dcdf520e34c8c; 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e up to, but not including, 9b02c5c4147f8af8ed783c8deb5df927a55c3951; 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e up to, but not including, cfcfa0ca0212162aa472551266038e8fd6768cff; 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e up to, but not including, 3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2; 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e up to, but not including, 4e8a0005d633a4adc98e3b65d5080f93b90d356b; 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e up to, but not including, 56145d237385ca0e7ca9ff7b226aaf2eb8ef368b; 6.0 | 529e685e522b9d7fb379dbe6929dcdf520e34c8c, 9b02c5c4147f8af8ed783c8deb5df927a55c3951, cfcfa0ca0212162aa472551266038e8fd6768cff, 3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2, 4e8a0005d633a4adc98e3b65d5080f93b90d356b, 56145d237385ca0e7ca9ff7b226aaf2eb8ef368b |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) | V3.1.6 and later; V3.1.5 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) | V3.1.6 and later; V3.1.5 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) | V3.1.6 and later; V3.1.5 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) | V3.1.6 and later; V3.1.5 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 TM MFP - GNU/Linux subsystem | all versions | Not stated |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) | V3.1.6 and later; V3.1.5 and later; V3.1.7 and later | Not stated |
| Linux | Linux Kernel | 6.0.1 up to, but not including, 6.1.167; 6.2 up to, but not including, 6.6.130; 6.7 up to, but not including, 6.12.77; 6.13 up to, but not including, 6.18.17; 6.19 up to, but not including, 6.19.7; 6.0; 7.0 | 6.1.167, 6.6.130, 6.12.77, 6.18.17, 6.19.7 |
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.
Official description
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim The root cause of this bug is that when 'bpf_link_put' reduces the refcount of 'shim_link->link.link' to zero, the resource is considered released but may still be referenced via 'tr->progs_hlist' in 'cgroup_shim_find'. The actual cleanup of 'tr->progs_hlist' in 'bpf_shim_tramp_link_release' is deferred. During this window, another process can cause a use-after-free via 'bpf_trampoline_link_cgroup_shim'. Based on Martin KaFai Lau's suggestions, I have created a simple patch. To fix this: Add an atomic non-zero check in 'bpf_trampoline_link_cgroup_shim'. Only increment the refcount if it is not already zero. Testing: I verified the fix by adding a delay in 'bpf_shim_tramp_link_release' to make the bug easier to trigger: static void bpf_shim_tramp_link_release(struct bpf_link *link) { /* ... */ if (!shim_link->trampoline) return; + msleep(100); WARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link, shim_link->trampoline, NULL)); bpf_trampoline_put(shim_link->trampoline); } Before the patch, running a PoC easily reproduced the crash(almost 100%) with a call trace similar to KaiyanM's report. After the patch, the bug no longer occurs even after millions of iterations.
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.
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2
- git.kernel.org/stable/c/4e8a0005d633a4adc98e3b65d5080f93b90d356b
- git.kernel.org/stable/c/529e685e522b9d7fb379dbe6929dcdf520e34c8c
- git.kernel.org/stable/c/56145d237385ca0e7ca9ff7b226aaf2eb8ef368b
- git.kernel.org/stable/c/9b02c5c4147f8af8ed783c8deb5df927a55c3951
- git.kernel.org/stable/c/cfcfa0ca0212162aa472551266038e8fd6768cff
Other references
Recent Use After Free vulnerabilities
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