[CVE-2026-64436][MODERATE 7.0] net: af_key: initialize alg_key_len for IPComp states

[CVE-2026-64436][MODERATE 7.0] net: af_key: initialize alg_key_len for IPComp states

[AL-KERNEL]

CVE: CVE-2026-64436
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: af_key: initialize alg_key_len for IPComp states
Commit: 58e82fc3dedb57b1432292504415b224fd2d6acb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=58e82fc3dedb57b1432292504415b224fd2d6acb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64436
Analysis date: Sat, 25 Jul 2026 10:33:20 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
An uninitialized `alg_key_len` in the AF_KEY IPComp path can make XFRM migration clone an oversized algorithm object, causing a local slab out-of-bounds read with DoS and possible limited kernel heap disclosure impact.

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

The original Linux kernel CVE announcement for CVE-2026-64436 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64436

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-64436	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-457;CWE-125;*CWE-200;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '5.8';DESCR 'An uninitialized alg_key_len field in the AF_KEY IPComp path can make xfrm_algo_clone compute an oversized algorithm object length during XFRM state migration. This causes kmemdup to read past the end of the allocated calg object and can trigger a slab out of bounds read from kernel heap memory. For the CVSS the PR:L is used in the paranoid score because CAP_NET_ADMIN may be delegated to a container, network namespace, or constrained service account rather than requiring full host root. The issue is local and not network reachable because it requires creating an IPComp SA through PF_KEY and then triggering XFRM_MSG_MIGRATE. Impact is at least local denial of service via kernel crash or failed migration, with plausible limited confidentiality impact if overread heap bytes are copied into state that can later be observed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	READ KASAN OOB HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Weak/indirect corruption candidate: +1. `alg_key_len` is uninitialized and later used to compute the `kmemdup()` size, causing a concrete slab out-of-bounds read.
* Reliable kernel crash / strong DoS: +1. KASAN shows a reproducible slab-out-of-bounds read in `kmemdup_noprof()`, and large garbage lengths can also make migration cloning fail.
* Confidentiality impact plausible: +1. The overread copies adjacent kernel heap bytes into a cloned algorithm object, so limited kernel heap disclosure is plausible if that state later becomes observable.
* Broad/default/common subsystem exposure: +1. XFRM/IPsec and PF_KEY are commonly built kernel networking components, even if the exact migration trigger is not a default workload.
* Requires CAP_NET_ADMIN in typical deployments: -1. Creating PF_KEY IPComp state and triggering XFRM migration normally requires CAP_NET_ADMIN, but namespace or service delegation can reduce this below full host-root in practical deployments.

Paranoid signals:

* Local unprivileged trigger: +1. On systems with unprivileged user namespaces and network namespaces enabled, an unprivileged user may obtain CAP_NET_ADMIN in a private netns and exercise XFRM/PF_KEY paths.
* Weak/indirect corruption candidate: +1. The primitive is a real kernel heap out-of-bounds read caused by an uninitialized length field, but not an OOB write or UAF.
* Reliable kernel crash / strong DoS: +1. The reported KASAN trace confirms an invalid slab read, and oversized copies or allocations can disrupt migration.
* Confidentiality impact plausible: +1. Adjacent heap data may be copied into the cloned XFRM algorithm object.
* Broad/default/common subsystem exposure: +1. XFRM/IPsec is not treated as rare-only for triage because it is a standard kernel networking security subsystem.

No privilege escalation bonus is awarded. There is no demonstrated write primitive, UAF reclaim, object replacement, callback control, refcount takeover, or arbitrary memory corruption.

## 3. Reachability analysis

The bug is local and control-plane reachable. The attacker needs to create an IPComp SA via PF_KEY and then trigger XFRM state migration through the netlink XFRM path. In typical host deployments this requires CAP_NET_ADMIN, so the conservative score treats it as privileged. In containerized or namespace-enabled deployments, CAP_NET_ADMIN may be delegated to a less trusted netns or service account, which supports the paranoid score.

The issue is not remotely packet-triggerable. It is not caused by inbound IPsec traffic alone. The affected path is reachable through local PF_KEY and XFRM management operations.

Call-site confidence: high. The commit gives the concrete chain `pfkey_msg2xfrm_state()` -> `xfrm_state_migrate()` -> `xfrm_state_clone_and_setup()` -> `xfrm_algo_clone()` -> `kmemdup()` and includes a KASAN trace.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it has a concrete kernel heap out-of-bounds read, not merely a validation or bookkeeping issue. Realistic impact is local DoS or failed XFRM migration, with plausible limited confidentiality exposure from copied heap bytes. It does not currently justify Important-class treatment by itself because there is no shown write primitive, UAF reclaim, type confusion, or credible LPE chain.

Overall this is an actionable Moderate and should not be auto-closed without review.

## 5. One-sentence report phrase

An uninitialized `alg_key_len` in the AF_KEY IPComp path can make XFRM migration clone an oversized algorithm object, causing a local slab out-of-bounds read with DoS and possible limited kernel heap disclosure impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because the patch fixes a concrete uninitialized length field that reaches `kmemdup()` as a copy size and produces a slab out-of-bounds read. The main question for human triage is whether copied heap bytes can be exposed through later XFRM state dumping or related user-visible paths.

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

Patch: net: af_key: initialize alg_key_len for IPComp states
Commit: 58e82fc3dedb57b1432292504415b224fd2d6acb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=58e82fc3dedb57b1432292504415b224fd2d6acb

Commit description:

pfkey_msg2xfrm_state() handles the IPComp (SADB_X_SATYPE_IPCOMP) case by
allocating x->calg and copying only the algorithm name:

	x->calg = kmalloc_obj(*x->calg);
	if (!x->calg) {
		err = -ENOMEM;
		goto out;
	}
	strcpy(x->calg->alg_name, a->name);
	x->props.calgo = sa->sadb_sa_encrypt;

Unlike the authentication (x->aalg) and encryption (x->ealg) branches of
the same function, the compression branch never initializes
calg->alg_key_len.  IPComp carries no key and the allocation only
reserves sizeof(struct xfrm_algo) (i.e. no room for a key), so the field
is left containing uninitialized slab data.

calg->alg_key_len is later used as a length by xfrm_algo_clone() when an
IPComp state is cloned during XFRM_MSG_MIGRATE:

	xfrm_state_migrate()
	  xfrm_state_clone_and_setup()
	    x->calg = xfrm_algo_clone(orig->calg);
	      kmemdup(orig, xfrm_alg_len(orig));

where xfrm_alg_len() returns sizeof(*alg) + (alg_key_len + 7) / 8.  With
a non-zero garbage alg_key_len, kmemdup() reads past the end of the
68-byte calg object.  Adding an IPComp SA via PF_KEY and then migrating
it triggers (net-next, KASAN, init_on_alloc=0):

  BUG: KASAN: slab-out-of-bounds in kmemdup_noprof+0x44/0x60
  Read of size 4164 at addr ff11000025a74980 by task diag2/9287
  CPU: 3 UID: 0 PID: 9287 Comm: diag2 7.1.0-rc6-g903db046d557 #1
  Call Trace:
   <TASK>
   dump_stack_lvl+0x10e/0x1f0
   print_report+0xf7/0x600
   kasan_report+0xe4/0x120
   kasan_check_range+0x105/0x1b0
   __asan_memcpy+0x23/0x60
   kmemdup_noprof+0x44/0x60
   xfrm_state_migrate+0x70a/0x1da0
   xfrm_migrate+0x753/0x18a0
   xfrm_do_migrate+0xb47/0xf10
   xfrm_user_rcv_msg+0x411/0xb50
   netlink_rcv_skb+0x158/0x420
   xfrm_netlink_rcv+0x71/0x90
   netlink_unicast+0x584/0x850
   netlink_sendmsg+0x8b0/0xdc0
   ____sys_sendmsg+0x9f7/0xb90
   ___sys_sendmsg+0x134/0x1d0
   __sys_sendmsg+0x16d/0x220
   do_syscall_64+0x116/0x7d0
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
   </TASK>

  Allocated by task 9287:
   kasan_save_stack+0x33/0x60
   kasan_save_track+0x14/0x30
   __kasan_kmalloc+0xaa/0xb0
   pfkey_add+0x2652/0x2ea0
   pfkey_process+0x6d0/0x830
   pfkey_sendmsg+0x42c/0x850
   __sys_sendto+0x461/0x4b0
   __x64_sys_sendto+0xe0/0x1c0
   do_syscall_64+0x116/0x7d0
   entry_SYSCALL_64_after_hwframe+0x77/0x7f

  The buggy address belongs to the object at ff11000025a74980
   which belongs to the cache kmalloc-96 of size 96
  The buggy address is located 0 bytes inside of
   allocated 68-byte region [ff11000025a74980, ff11000025a749c4)

Depending on the uninitialized value the same field can instead request
an oversized kmemdup() allocation and make the migration clone fail.

The XFRM netlink path is not affected: verify_one_alg() rejects an
XFRMA_ALG_COMP attribute shorter than xfrm_alg_len(), so a calg added via
XFRM_MSG_NEWSA is always self-consistent.


[Commit description truncated; see the upstream URL below]

Changed files:
  net/key/af_key.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=58e82fc3dedb57b1432292504415b224fd2d6acb

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

The original Linux kernel CVE announcement for CVE-2026-64436 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64436

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:H/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 3
  Paranoid ActionableScore: 5

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: NO
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).