[CVE-2026-74569][IMPORTANT] netfilter: nf_conntrack_sip: widen NAT rewrite delta to s32 in sip_help_tcp() [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-74569
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: netfilter: nf_conntrack_sip: widen NAT rewrite delta to s32 in sip_help_tcp() [ Upstream
Commit: 63eea41759fd682229c14e0a2205802b46d106f3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=63eea41759fd682229c14e0a2205802b46d106f3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74569
Analysis date: Sat, 15 Aug 2026 12:33:14 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A signed 16 bit NAT rewrite delta overflow in nf_conntrack_sip can let remote SIP TCP traffic processed by the SIP helper make datalen wrap and trigger a use-after-free read in ct_sip_get_header(), causing a kernel crash and requiring manual review due to network-reachable memory corruption.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74569 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74569

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: IMPORTANT
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-74569	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-190;CWE-125;*CWE-416;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A signed 16 bit overflow in the SIP TCP conntrack helper can occur when NAT rewriting expands a SIP message by more than S16_MAX bytes while the packet remains below the 65535 byte skb enlargement limit. The wrapped diff can make datalen become a huge unsigned value, causing ct_sip_get_header to read past the linearized skb tail and hit a use-after-free read in softirq packet processing. For the CVSS the PR:N is used because a remote sender only needs network reachability to a host where the SIP TCP conntrack helper and NAT path process the traffic. The issue is network reachable but depends on SIP helper and NAT configuration, so AC:H is used for the base and paranoid scores. Impact is at least remote denial of service via kernel crash. For the paranoid score, C:L/I:L/A:H is the highest still defensible interpretation because the bug is a network reachable UAF read in a protocol parser, but no arbitrary write primitive is proven.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	READ DANGER NETFILTER UAF SKB IPV6 KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative scoring:

* Remote reachable / network-triggerable: +2. A remote sender can influence SIP TCP traffic processed by nf_conntrack_sip and nf_nat_sip when the helper and NAT path are enabled.
* Memory corruption, weak/indirect corruption candidate: +1. The signed s16 overflow makes datalen become a huge unsigned value and causes ct_sip_get_header() to read past the linearized skb tail. The demonstrated primitive is read-side OOB/UAF, not an arbitrary write.
* Real lifetime corruption: +1. The KASAN report explicitly shows use-after-free in ct_sip_get_header().
* Reliable kernel crash / strong DoS: +1. The bug is hit in softirq packet processing and is likely to produce an Oops or panic under KASAN or hardened production settings.
* Common networking core path or packet-processing path: +1. This is in the netfilter conntrack/NAT packet path, although the SIP helper configuration is required.

Paranoid delta:

* Upgrade weak memory-corruption candidate to generic memory corruption: +1 net increase. The KASAN UAF read occurs in a remotely influenced protocol parser and should not be auto-closed without manual review, even though no write primitive or reclaim primitive is demonstrated.

Not awarded:

* No Strong LPE plausibility. There is no demonstrated attacker-controlled reclaim, overwrite, callback control, type confusion, or refcount takeover.
* No Dirty-Pipe-like or page-cache ownership violation.
* No admin privilege penalty. The attacker does not need local administrative privileges if the target network path processes the SIP traffic.
* No rare-subsystem penalty. The trigger depends on SIP helper/NAT configuration, but netfilter packet processing is not a rare kernel subsystem.

Call-site confidence: high. The provided stack trace shows the concrete path through sip_help_tcp(), nf_confirm(), nf_hook_slow(), IPv6 forwarding, and softirq receive processing.

## 3. Reachability analysis

The bug is remotely triggerable when TCP SIP traffic is handled by nf_conntrack_sip with NAT rewriting enabled. The attacker needs network reachability to a path where the firewall/router processes the crafted SIP message, not local code execution on the victim.

The path is configuration-dependent. Many modern deployments do not automatically enable protocol helpers for all traffic, and SIP ALG/NAT helper use may be disabled or limited. However, when enabled on a firewall, router, gateway, or container host, the bug can be reached through ordinary packet forwarding or local packet output paths.

Namespaces do not materially reduce the remote case. For local/container scenarios, CAP_NET_ADMIN may be needed to configure the helper, but not necessarily to send traffic once the vulnerable helper path is already active.

## 4. Severity interpretation

This is above an ordinary Moderate because it combines network reachability, netfilter packet-path exposure, integer overflow, and a demonstrated KASAN use-after-free read. The most realistic impact is remote denial of service via kernel crash.

Theoretical escalation beyond DoS is not strongly supported. The patch and trace show read past skb bounds / UAF read, but not an attacker-controlled write, object replacement, function pointer overwrite, or privilege escalation chain. Therefore the conservative score is Actionable Moderate, while the paranoid score reaches Strong Important candidate mainly because network-reachable kernel UAFs should receive manual review.

## 5. One-sentence report phrase

A signed 16 bit NAT rewrite delta overflow in nf_conntrack_sip can let remote SIP TCP traffic processed by the SIP helper make datalen wrap and trigger a use-after-free read in ct_sip_get_header(), causing a kernel crash and requiring manual review due to network-reachable memory corruption.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is network reachable under realistic SIP helper/NAT configurations and has a concrete KASAN use-after-free read in the netfilter packet path, even though the demonstrated practical impact is mainly DoS.

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: netfilter: nf_conntrack_sip: widen NAT rewrite delta to s32 in sip_help_tcp() [ Upstream
Commit: 63eea41759fd682229c14e0a2205802b46d106f3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=63eea41759fd682229c14e0a2205802b46d106f3

Changed files:
  net/netfilter/nf_conntrack_sip.c
  net/netfilter/nf_conntrack_proto.c
  net/netfilter/core.c
  net/ipv6/ip6_output.c
  net/ipv6/ip6_input.c
  net/core/dev.c
  kernel/softirq.c
  include/linux/netfilter/nf_conntrack_sip.h
  net/netfilter/nf_nat_sip.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=63eea41759fd682229c14e0a2205802b46d106f3

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DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-74569 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74569

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 7

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 6
  Paranoid ActionableScore: 7

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).