CVE-2026-43027
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Use-After-Free in Linux Kernel Netfilter Conntrack Helper

Publication date: 2026-05-01

Last updated on: 2026-05-08

Assigner: kernel.org

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)
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Meta Information
Published
2026-05-01
Last Modified
2026-05-08
Generated
2026-06-16
AI Q&A
2026-05-01
EPSS Evaluated
2026-06-14
NVD
CVE-2026-43027
EUVD
EUVD-2026-26626
Affected Vendors & Products
Showing 13 associated CPEs
Vendor Product Version / Range
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel From 5.11 (inc) to 5.15.203 (exc)
linux linux_kernel From 6.13 (inc) to 6.18.22 (exc)
linux linux_kernel From 5.16 (inc) to 6.1.168 (exc)
linux linux_kernel From 4.14 (inc) to 5.10.253 (exc)
linux linux_kernel From 6.19 (inc) to 6.19.12 (exc)
linux linux_kernel From 6.7 (inc) to 6.12.81 (exc)
linux linux_kernel From 6.2 (inc) to 6.6.134 (exc)
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-416 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.
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Executive Summary

This vulnerability exists in the Linux kernel's netfilter component, specifically in the nf_conntrack_helper module. The issue arises because the function nf_conntrack_helper_unregister() calls nf_ct_expect_iterate_destroy() to remove expectations related to a helper being unregistered, but it incorrectly passes NULL instead of the actual helper pointer. As a result, the expectations are not properly cleaned up and remain after the helper is freed. Subsequent operations then dereference this freed helper pointer, causing a use-after-free error, which can lead to kernel crashes or other unpredictable behavior.

Impact Analysis

The vulnerability can cause a use-after-free condition in the Linux kernel, which may lead to system instability, crashes, or potential exploitation by attackers. Since the kernel dereferences freed memory, it could be manipulated to execute arbitrary code or cause denial of service, impacting the reliability and security of systems running vulnerable Linux kernel versions.

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