[CVE-2026-64114][MODERATE 7.0] ipv4: raw: reject IP_HDRINCL packets with ihl < 5

[CVE-2026-64114][MODERATE 7.0] ipv4: raw: reject IP_HDRINCL packets with ihl < 5

[AL-KERNEL]

CVE: CVE-2026-64114
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ipv4: raw: reject IP_HDRINCL packets with ihl < 5
Commit: 1065b9efa4126df559b03a849c139ecfae92cd25
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1065b9efa4126df559b03a849c139ecfae92cd25
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64114
Analysis date: Sun, 19 Jul 2026 21:41:16 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
Malformed IP_HDRINCL packets with IPv4 IHL less than 5 can enter the local output path and trigger an OOB memcpy-sized access in AH processing, causing a reproducible kernel panic and requiring manual review for possible memory-corruption impact.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-64114 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64114

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: MODERATE 7.0
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
======================================================================

CVE-2026-64114	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-20;CWE-125;*CWE-787;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'Malformed IPv4 packets sent through raw IP_HDRINCL sockets can enter the local IPv4 output path with IHL less than 5. Downstream IPv4/AH processing may subtract sizeof(struct iphdr) from the short header length and pass a negative value converted to size_t into memcpy, causing an out-of-bounds kernel memory access and a crash. For the CVSS the PR:L is used because reliable triggering needs a local process with CAP_NET_RAW and in the demonstrated AH path also net namespace or CAP_NET_ADMIN style control for xfrm policy setup, which can be available to an unprivileged local user on systems with user namespaces or delegated container capabilities. The issue is not directly network reachable from a remote host because the malformed packet is injected locally through a raw socket rather than received as normal network traffic. Impact is at least local denial of service via kernel panic, and the paranoid assessment treats the memcpy based OOB access as memory corruption that may require manual review for confidentiality or integrity impact.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	REMOTE KASAN OOB NETWORK KERNEL_PANIC_PLUS_UAF LINUS TEST IPV6 KPANIC PACKET  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative scoring:

* +1 Local unprivileged trigger: malformed IP_HDRINCL traffic can be generated by a local process with CAP_NET_RAW, and user plus net namespaces may provide this capability without full host root.
* +1 Memory corruption, weak/indirect candidate: the patch describes an OOB memcpy-sized access caused by ihl less than 5, but the demonstrated result is kernel panic rather than a controlled write primitive.
* +1 Reliable kernel crash / strong DoS: the issue was reproduced with KASAN and also in a rootless Docker-like setup with NET_ADMIN capability.
* +1 Common networking path: the malformed packet enters IPv4 local output and XFRM/AH processing, which are kernel networking paths that should not be auto-dismissed as obscure.

Paranoid additions:

* +1 Upgrade from weak to strong corruption concern: memcpy with a size derived from a negative length converted to size_t is a concrete OOB kernel memory access and deserves manual review.
* +1 Weak LPE concern: privilege escalation is not demonstrated, but the corruption sink is in kernel networking code and is stronger than a simple NULL dereference.
* +1 Broad exposure concern: IPv4 raw sockets, user namespaces, containers, and XFRM/IPsec are common enough that this should not be treated as a rare hardware or legacy-only path.

Not counted:

* +0 Remote reachable: this is not directly triggered by packets received from the network.
* +0 Real lifetime corruption: no UAF, refcount, RCU, or stale pointer lifetime primitive is shown.
* +0 Dirty-Pipe-like primitive: no page-cache or COW ownership bypass is shown.
* +0 Availability impact extra point: reliable crash is already counted, so DoS is not double-counted.

## 3. Reachability analysis

The direct trigger is local raw IPv4 packet injection with IP_HDRINCL and ihl less than 5. The demonstrated AH crash also requires a matching XFRM AH policy on the outgoing route and a real netdev because loopback bypasses the relevant XFRM output path.

This is not a remote network attack against normal packet receive processing. However, it can be reachable from a reduced-privilege local or container context when user namespaces and network namespaces are enabled, because CAP_NET_RAW and CAP_NET_ADMIN may exist inside the namespace without full host-root privileges. If a product disables unprivileged user namespaces or blocks raw sockets/XFRM policy setup in containers, the practical reachability is lower.

## 4. Severity interpretation

This is above ordinary Moderate because the patch prevents a malformed local IPv4 header from reaching downstream AH processing where it causes an OOB memcpy-sized kernel access and a reproducible host crash. Realistic demonstrated impact is local DoS.

The Important-candidate argument is paranoid but defensible: the failure mode is a concrete OOB kernel memory access in networking code, not merely a WARN or validation cleanup. There is no demonstrated arbitrary write, controlled reclaim, or reliable LPE path, so the conservative score stays borderline. Still, the bug should not be auto-closed without manual review.

## 5. One-sentence report phrase

Malformed IP_HDRINCL packets with IPv4 IHL less than 5 can enter the local output path and trigger an OOB memcpy-sized access in AH processing, causing a reproducible kernel panic and requiring manual review for possible memory-corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the issue is locally reachable in namespace/container configurations and reaches a concrete OOB kernel memory access in the IPv4/XFRM/AH path, with demonstrated kernel panic and plausible but unproven higher-impact corruption concerns.

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

Patch: ipv4: raw: reject IP_HDRINCL packets with ihl < 5
Commit: 1065b9efa4126df559b03a849c139ecfae92cd25
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1065b9efa4126df559b03a849c139ecfae92cd25

Commit description:

raw_send_hdrinc() validates that the caller-supplied IPv4 header
fits within the message length:

    iphlen = iph->ihl * 4;
    err = -EINVAL;
    if (iphlen > length)
        goto error_free;

    if (iphlen >= sizeof(*iph)) {
        /* fix up saddr, tot_len, id, csum, transport_header */
    }

It does not, however, reject ihl < 5.  For such a packet the
"if (iphlen >= sizeof(*iph))" branch is skipped, leaving the
crafted iphdr untouched, but the packet is still handed to
__ip_local_out() and onward.  Downstream consumers that read
iph->ihl assume a sane value: net/ipv4/ah4.c:ah_output() in
particular subtracts sizeof(struct iphdr) from top_iph->ihl * 4
and passes the (signed-int-negative, then cast to size_t)
result to memcpy(), producing an OOB access of length close to
SIZE_MAX and a host kernel panic.

An IPv4 header with ihl < 5 is malformed by definition (RFC 791:
"Internet Header Length is the length of the internet header in
32 bit words ... Note that the minimum value for a correct header
is 5.").  The kernel should not be willing to inject such a
packet into its own output path.

Reject "iphlen < sizeof(*iph)" alongside the existing
"iphlen > length" check.  This matches the principle that locally
constructed packets that re-enter the IP stack must pass the same
basic sanity tests that a foreign packet would be subjected to.

Once this lands, the "if (iphlen >= sizeof(*iph))" wrapper around
the fixup branch becomes redundant; left in place to keep the
patch minimal and backport-friendly.  A follow-up can unwrap it.

Note that commit 86f4c90 ("ipv4, ipv6: ensure raw socket
message is big enough to hold an IP header") ensures the message
buffer is large enough to hold an iphdr, but does not constrain
the self-reported iph->ihl.

Reachability: the malformed packet source is any caller with
CAP_NET_RAW, including an unprivileged process in a user+net
namespace on a kernel with CONFIG_USER_NS=y.  The reproduced AH
crash also requires a matching xfrm AH policy on the outgoing
route; a container granted CAP_NET_ADMIN can install that state
and policy in its netns.  Loopback bypasses xfrm_output, so the
trigger uses a real netdev.

Reproduced on UML + KASAN: kernel-mode fault at addr 0x0 with
memcpy_orig at the crash site.  Same shape reproduces inside a
rootless Docker container with --cap-add NET_ADMIN on a stock
distro kernel.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Suggested-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Link: https://patch.msgid.link/77ec2b5e8111961c2c39883c92e8aa2709039c17.1778614451.git.michael.bommarito@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv4/ah4.c
  net/ipv4/raw.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=1065b9efa4126df559b03a849c139ecfae92cd25

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

The original Linux kernel CVE announcement for CVE-2026-64114 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64114

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:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/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: 4
  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: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).