[CVE-2026-72220][IMPORTANT] sunrpc: harden rq_procinfo lifecycle to prevent double-free

[CVE-2026-72220][IMPORTANT] sunrpc: harden rq_procinfo lifecycle to prevent double-free

[AL-KERNEL]

CVE: CVE-2026-72220
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: sunrpc: harden rq_procinfo lifecycle to prevent double-free
Commit: 66014ab165cb01bfef5836939412a8ef98d5d5ff
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=66014ab165cb01bfef5836939412a8ef98d5d5ff
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72220
Analysis date: Sat, 15 Aug 2026 06:29:22 -0400
ActionableScore: 9
ActionableScore lower bound: 8
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A stale rq_procinfo pointer in SUNRPC request handling can cause pc_release to be invoked again on released or reused RPC state, allowing a remote client to trigger double-free or use-after-free conditions and at least a kernel crash on exposed RPC services.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72220 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72220

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-2026-72220	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-415;*CWE-416;*CWE-664;*CWE-672;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'A stale rq_procinfo pointer in the SUNRPC server request object can cause svc_release_rqst to invoke a previous pc_release callback against already released or reused RPC state. A remote client may be able to trigger this by sending a malformed or unsupported RPC request after a prior request has installed a valid procinfo, so the next early error path reaches release handling before a new procinfo is installed. For the CVSS the PR:N is used because no local account or authenticated privilege on the target is required when the affected SUNRPC service is reachable over the network. The attack is network reachable for exposed RPC services such as NFS server deployments, although practical exposure is usually limited to trusted storage or internal networks. Impact is at least remote denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact because the bug class is double free or use after free memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 9)  SKIP CVE-2026-72220 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: d9adbb6e10bf7d4223d3d521ede1b2052903bc5e YES  NO NO unknown 	MAYBE	REMOTE DANGER ERRORPATH UAF NETWORK KPANIC 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=9
ActionableScoreLower=8

## 1. ActionableScore

* Conservative score: 8
* Paranoid score: 9
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. SUNRPC request processing can be reached over the network when an RPC service such as NFS server is exposed.
* Generic memory corruption, strong corruption primitive: +2. The commit explicitly describes double-free or use-after-free caused by stale rq_procinfo reuse.
* Real lifetime corruption: +1. The bug is a stale lifecycle pointer and release callback issue across reused svc_rqst objects.
* Reliable kernel crash / strong DoS: +1. Re-invoking pc_release against released state can plausibly crash the kernel.
* Weak LPE concern: +1. UAF or double-free exists, but the patch does not show attacker-controlled reclaim, arbitrary write, or controlled callback target.
* Broad/common subsystem exposure: +1. SUNRPC/NFS server deployments are common in enterprise and storage environments.

Paranoid delta:

* Strong LPE plausibility instead of weak LPE concern: +2 instead of +1. This is defensible because stale release callback reuse combined with double-free/UAF in a network service is a high-risk lifetime primitive, even though exploit control is not demonstrated.

No subtraction applied:

* No admin privilege requirement is needed for the remote client if the service is reachable.
* No hard race penalty is applied because the issue is primarily stale state reuse across requests, not a narrow timing-only race.
* No rare subsystem penalty is applied because SUNRPC/NFS is a common server-side kernel subsystem.

Call-site confidence: high. The patch shows svc_release_rqst(), svc_process(), and svc_process_bc() lifecycle points directly.

## 3. Reachability analysis

A remote RPC client can potentially trigger the vulnerable path by sending a valid request that installs rq_procinfo followed by a malformed or unsupported request that reaches an early error path before a new rq_procinfo is installed. The issue is relevant mainly on systems running SUNRPC services, especially NFS server deployments. These services are often restricted to internal storage or data-center networks, but they are still network-facing when enabled.

Namespaces and containers do not materially reduce the remote attack requirement. The attacker does not need a local account on the target if the RPC service is reachable. Practical exploitation beyond DoS would depend on allocator behavior, object reuse, and whether the double-free or UAF can be shaped into a controlled primitive.

## 4. Severity interpretation

This behaves like an Important-class candidate rather than an ordinary Moderate issue. The realistic demonstrated impact is remote kernel crash or denial of service. The theoretical higher impact is stronger because the bug class is explicit double-free/use-after-free in kernel network request processing.

The patch does not demonstrate arbitrary code execution, controlled reclaim, or a reliable privilege escalation primitive. However, network-reachable lifetime corruption with stale release callback reuse is too risky to auto-close as ordinary Moderate.

## 5. One-sentence report phrase

A stale rq_procinfo pointer in SUNRPC request handling can cause pc_release to be invoked again on released or reused RPC state, allowing a remote client to trigger double-free or use-after-free conditions and at least a kernel crash on exposed RPC services.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is network-reachable kernel memory lifetime corruption with explicit double-free/use-after-free semantics in SUNRPC server request handling. Even if the most realistic impact is DoS, the bug class and exposure justify manual review for possible exploitability beyond crash.

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

Patch: sunrpc: harden rq_procinfo lifecycle to prevent double-free
Commit: 66014ab165cb01bfef5836939412a8ef98d5d5ff
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=66014ab165cb01bfef5836939412a8ef98d5d5ff

Commit description:

The svc_release_rqst() function executes the callback inside
rqstp->rq_procinfo->pc_release. However, if a worker thread begins
processing a new request and encounters an early error path (e.g.,
unsupported protocol, short frame, or bad auth) before a valid
rq_procinfo is installed, a stale release hook can be re-triggered
against reused state from the previous RPC, resulting in a double-free
or use-after-free vulnerability.

Harden the lifecycle of rq_procinfo by:
1. Ensuring svc_release_rqst() always clears rq_procinfo after the
   optional pc_release() call, regardless of whether the hook exists.
2. Explicitly clearing rq_procinfo at request entry in svc_process()
   before any early decode or drop paths.
3. Ensuring svc_process_bc() does the same at backchannel entry.

This guarantees that error flows will not encounter a non-NULL stale
rq_procinfo pointer when there is nothing to release.

Fixes: d9adbb6 ("sunrpc: delay pc_release callback until after the reply is sent")
Cc: stable@vger.kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Suggested-by: Chuck Lever <cel@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Luxiao Xu <rakukuip@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/sunrpc/svc.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=66014ab165cb01bfef5836939412a8ef98d5d5ff

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

The original Linux kernel CVE announcement for CVE-2026-72220 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72220

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 8
  Paranoid ActionableScore: 9

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).