Linux: Use After Free
CVE-2026-43027 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 5cf28d5c8dcbbe8af6d3b145babe491906d7bad1, 504ba4168466c91210c45acdc332479cfd5f2da6, dc1739eff48e34cc71d4e2f03715493fbcebd8af 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 5cf28d5c8dcbbe8af6d3b145babe491906d7bad1 or 504ba4168466c91210c45acdc332479cfd5f2da6 or dc1739eff48e34cc71d4e2f03715493fbcebd8af or 2cf2737c85a2ba2b52024dafe68ffad2676f97be, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.10.253 or 5.15.203 or 6.1.168 or 6.6.134, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | ac7b848390036dadd4351899d2a23748075916bd up to, but not including, 5cf28d5c8dcbbe8af6d3b145babe491906d7bad1; ac7b848390036dadd4351899d2a23748075916bd up to, but not including, 504ba4168466c91210c45acdc332479cfd5f2da6; ac7b848390036dadd4351899d2a23748075916bd up to, but not including, dc1739eff48e34cc71d4e2f03715493fbcebd8af; ac7b848390036dadd4351899d2a23748075916bd up to, but not including, 2cf2737c85a2ba2b52024dafe68ffad2676f97be; ac7b848390036dadd4351899d2a23748075916bd up to, but not including, 2c16e4d64dd91227742dfe196a3e7b0568bef65a; ac7b848390036dadd4351899d2a23748075916bd up to, but not including, 620f3d14c1ef51d425060a3056ad8dbae8f998a3; ac7b848390036dadd4351899d2a23748075916bd up to, but not including, 90bd7e8501349db3006d21fbc09df9ffcb172965; ac7b848390036dadd4351899d2a23748075916bd up to, but not including, a242a9ae58aa46ff7dae51ce64150a93957abe65; and 1 more ranges | 5cf28d5c8dcbbe8af6d3b145babe491906d7bad1, 504ba4168466c91210c45acdc332479cfd5f2da6, dc1739eff48e34cc71d4e2f03715493fbcebd8af, 2cf2737c85a2ba2b52024dafe68ffad2676f97be, 2c16e4d64dd91227742dfe196a3e7b0568bef65a, 620f3d14c1ef51d425060a3056ad8dbae8f998a3 |
| 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 | 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 | 4.14 up to, but not including, 5.10.253; 5.11 up to, but not including, 5.15.203; 5.16 up to, but not including, 6.1.168; 6.2 up to, but not including, 6.6.134; 6.7 up to, but not including, 6.12.81; 6.13 up to, but not including, 6.18.22; 6.19 up to, but not including, 6.19.12; 7.0 | 5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81, 6.18.22 |
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: netfilter: nf_conntrack_helper: pass helper to expect cleanup nf_conntrack_helper_unregister() calls nf_ct_expect_iterate_destroy() to remove expectations belonging to the helper being unregistered. However, it passes NULL instead of the helper pointer as the data argument, so expect_iter_me() never matches any expectation and all of them survive the cleanup. After unregister returns, nfnl_cthelper_del() frees the helper object immediately. Subsequent expectation dumps or packet-driven init_conntrack() calls then dereference the freed exp->helper, causing a use-after-free. Pass the actual helper pointer so expectations referencing it are properly destroyed before the helper object is freed. BUG: KASAN: slab-use-after-free in string+0x38f/0x430 Read of size 1 at addr ffff888003b14d20 by task poc/103 Call Trace: string+0x38f/0x430 vsnprintf+0x3cc/0x1170 seq_printf+0x17a/0x240 exp_seq_show+0x2e5/0x560 seq_read_iter+0x419/0x1280 proc_reg_read+0x1ac/0x270 vfs_read+0x179/0x930 ksys_read+0xef/0x1c0 Freed by task 103: The buggy address is located 32 bytes inside of freed 192-byte region [ffff888003b14d00, ffff888003b14dc0)
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: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/2c16e4d64dd91227742dfe196a3e7b0568bef65a
- git.kernel.org/stable/c/2cf2737c85a2ba2b52024dafe68ffad2676f97be
- git.kernel.org/stable/c/504ba4168466c91210c45acdc332479cfd5f2da6
- git.kernel.org/stable/c/5cf28d5c8dcbbe8af6d3b145babe491906d7bad1
- git.kernel.org/stable/c/620f3d14c1ef51d425060a3056ad8dbae8f998a3
- git.kernel.org/stable/c/90bd7e8501349db3006d21fbc09df9ffcb172965
- git.kernel.org/stable/c/a242a9ae58aa46ff7dae51ce64150a93957abe65
- git.kernel.org/stable/c/dc1739eff48e34cc71d4e2f03715493fbcebd8af
Other references
Recent Use After Free vulnerabilities
- 8.1 High severity
- 8.1 High severity
- 7.8 High severity
- 7.0 High severity
- 7.8 High severity
- 7.8 High severity
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