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Linux KernelOperating system · Linux

CVE-2026-53349

MEDIUM · 5.5 CVSS v3.1 Published 2026-07-01
Fix available
A fix is available. Upgrade to 6.1.176 / 6.6.143 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click Patch available 7 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack: destroy stale expectfn expectations on unregister NAT helpers such as nf_nat_h323 store a raw pointer to module text in exp->expectfn (e.g. ip_nat_q931_expect). nf_ct_helper_expectfn_unregister() only unlinks the callback descriptor and never walks the expectation table, so an expectation pending at module removal survives with a dangling exp->expectfn into freed module text. When the expected connection arrives, init_conntrack() invokes exp->expectfn(), now a stale pointer into the unloaded module. Reproduced on a KASAN build by loading the H.323 helpers, creating a Q.931 expectation, unloading nf_nat_h323, then connecting to the expected port: Oops: int3: 0000 [#1] SMP KASAN NOPTI RIP: 0010:0xffffffffa06102d1 init_conntrack.isra.0 (net/netfilter/nf_conntrack_core.c:1862) nf_conntrack_in (net/netfilter/nf_conntrack_core.c:2049) ipv4_conntrack_local (net/netfilter/nf_conntrack_proto.c:223) nf_hook_slow (net/netfilter/core.c:619) __ip_local_out (net/ipv4/ip_output.c:120) __tcp_transmit_skb (net/ipv4/tcp_output.c:1715) tcp_connect (net/ipv4/tcp_output.c:4374) tcp_v4_connect (net/ipv4/tcp_ipv4.c:345) __sys_connect (net/socket.c:2167) Modules linked in: nf_conntrack_h323 [last unloaded: nf_nat_h323] Reaching the dangling state requires CAP_SYS_MODULE in the initial user namespace to remove a NAT helper that still has live expectations, so this is a robustness fix; leaving an expectation pointing at freed text is wrong regardless. Add nf_ct_helper_expectfn_destroy(), which walks the expectation table and drops every expectation whose ->expectfn matches the descriptor being torn down. Call it from each NAT helper's exit path after the existing RCU grace period, so no expectation outlives the code it points at and no extra synchronize_rcu() is introduced. With the fix, the same reproducer runs to completion without the Oops.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A dangling pointer vulnerability in Linux kernel's netfilter nf_conntrack module where NAT helpers (e.g., nf_nat_h323) store raw function pointers in exp->expectfn. When a helper is unloaded while expectations exist, the pointer becomes stale. Later, when init_conntrack() invokes the dangling exp->expectfn for a matching connection, it crashes executing freed module text.

MitigationApply the kernel patch adding nf_ct_helper_expectfn_destroy() to clean up expectations before module removal. Until patched, avoid unloading NAT helpers (nf_nat_h323, etc.) while active expectations exist in the connection tracking table.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 2.6.20, < 6.1.176>= 6.2, < 6.6.143>= 6.7, < 6.12.94>= 6.13, < 6.18.36>= 6.19, < 7.0.13= 7.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check kernel version against affected ranges
    Run 'uname -r' or 'cat /proc/version' to get the kernel version. Compare against: < 6.1.176, >= 6.2 and < 6.6.143, >= 6.7 and < 6.12.94, >= 6.13 and < 6.18.36, >= 6.19 and < 7.0.13, or 7.1
    Affected if The kernel version falls within any of the affected version ranges
  2. Identify loaded NAT helper modules
    Run 'lsmod | grep nf_nat' or check /proc/modules for modules like nf_nat_h323, nf_nat_ftp, nf_nat_sip, nf_nat_pptp, nf_nat_tftp or similar NAT helper modules
    Affected if Any NAT helper modules (nf_nat_*) are currently loaded
  3. List active conntrack expectations
    Run 'conntrack -L expect' or 'conntrack -E expect' to list all active connection tracking expectations in the system
    Affected if There are active expectations in the conntrack table, particularly those referencing NAT helpers
  4. Check for recently unloaded NAT helper modules
    Review system logs (dmesg, journalctl) for messages indicating NAT helper module unloading, or compare current loaded modules against known baseline
    Affected if A NAT helper module was unloaded while active expectations existed in the conntrack table

You are affected if your kernel version is within the affected ranges AND you have NAT helpers loaded with active conntrack expectations that may have persisted through a helper module unload event.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 6.1.176 / 6.6.143 / 6.12.94 or later
Fixed in 6.1.1766.6.1436.12.94
Vendor patch git.kernel.org →
Interim mitigation

Apply the kernel patch adding nf_ct_helper_expectfn_destroy() to clean up expectations before module removal. Until patched, avoid unloading NAT helpers (nf_nat_h323, etc.) while active expectations exist in the connection tracking table.

Recommended fix High confidence

Linux kernel 6.1.176, 6.6.143, 6.12.94, or 6.18.36 (or later stable releases)

  1. Identify the current kernel version using `uname -r` or `cat /proc/version`
  2. Determine which major kernel series you are running (e.g., 6.1.x, 6.2.x, 6.7.x, 6.13.x)
  3. For kernels 2.6.20 through 6.1.x: upgrade to kernel version 6.1.176 or later
  4. For kernels 6.2.x: upgrade to kernel version 6.6.143 or later
  5. For kernels 6.7.x through 6.11.x: upgrade to kernel version 6.12.94 or later
  6. For kernels 6.13.x through 6.17.x: upgrade to kernel version 6.18.36 or later
  7. Alternatively, upgrade to the latest stable kernel available from your distribution (6.12+ or 6.18+ recommended)
  8. Reboot into the new kernel to apply the fix
Caveat Kernel upgrades may introduce compatibility changes; ensure dependent modules and drivers support the target kernel version before upgrading production systems

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Linux Kernel Scoped from the published advisory
  • Consultation2.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
20.0 hours of engineering $3,460
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

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Peer-ranked notes from engineers who’ve handled CVE-2026-53349 in production — separate from our analysis above.

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