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CVE Record

CVE-2026-43027: netfilter: nf_conntrack_helper: pass helper to expect cleanup

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)

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2026-43027 is a Linux kernel memory safety bug in netfilter connection tracking helpers. A helper can be freed while related expectations still reference it, creating a kernel use-after-free. The sources do not provide CVSS, active exploitation evidence, or required attacker privileges.

Executive priority

Treat as a kernel patch-management item with uncertain severity. Prioritize internet-facing, security-sensitive, and appliance-like Linux systems once vendor-fixed kernels are available, but do not classify as emergency based on the supplied evidence alone.

Technical view

nf_conntrack_helper_unregister() passed NULL into nf_ct_expect_iterate_destroy(), so expectations for the unregistering helper were not removed. After nfnl_cthelper_del() freed the helper, expectation dumps or packet-driven init_conntrack() could dereference exp->helper after free. Kernel stable commits pass the helper pointer so matching expectations are destroyed before free.

Likely exposure

Likely exposure is Linux systems running affected kernel builds with netfilter conntrack helper functionality present. The source lists Linux as affected across multiple kernel lines, but does not provide distribution package names, CVSS, privilege requirements, or remote attackability.

Exploitation context

The bundle states KEV is false and provides no cited evidence of active exploitation. It includes a KASAN use-after-free trace from a proof-of-concept context, but not enough detail to assess practical exploitation or impact beyond kernel memory safety risk.

Researcher notes

The core bug is stale expectation state after helper unregister, leading to exp->helper use-after-free during seq dump or packet-driven connection tracking. The source lacks CVSS, CWE, exploit prerequisites, namespace details, and downstream fixed package data.

Mitigation direction

  • Apply vendor or distribution kernel updates containing the referenced stable fixes.
  • Review Siemens ProductCERT advisories if managing Siemens affected environments.
  • Check Linux kernel stable commits for the exact backport relevant to your kernel line.
  • If no vendor update is available, follow vendor guidance rather than applying ad hoc changes.

Validation and detection

  • Inventory Linux kernel versions across servers, appliances, and embedded systems.
  • Confirm whether installed kernels include one of the referenced stable fix commits.
  • Review netfilter conntrack helper usage where operational visibility is available.
  • Monitor vendor advisories for affected package names and fixed release numbers.
Prepared
Confidence
medium
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2026-43027 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
1ADP providers
11Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxac7b848390036dadd4351899d2a23748075916bd, ac7b848390036dadd4351899d2a23748075916bd, ac7b848390036dadd4351899d2a23748075916bd, ac7b848390036dadd4351899d2a23748075916bd, ac7b848390036dadd4351899d2a23748075916bd, ac7b848390036dadd4351899d2a23748075916bd, ac7b848390036dadd4351899d2a23748075916bd, ac7b848390036dadd4351899d2a23748075916bdunaffected
LinuxLinux4.14, 0, 5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81, 6.18.22, 6.19.12, 7.0affected
Weakness

CWE details

No CWE listed

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