[CVE-2026-63888][IMPORTANT] scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd() [ Upstream

[CVE-2026-63888][IMPORTANT] scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-63888
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd() [ Upstream
Commit: f7948af0dd03de84079dcd4dc215a69fd6fbb95d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f7948af0dd03de84079dcd4dc215a69fd6fbb95d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63888
Analysis date: Sun, 19 Jul 2026 20:55:29 -0400
ActionableScore: 9
ActionableScore lower bound: 7
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A remote iSCSI initiator can trigger a Text PDU DataDigest handling flaw that causes a 4 byte CRC overread and a stale pointer double-free, leading to remote kernel crash and possible allocator corruption on less hardened kernels.

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

The original Linux kernel CVE announcement for CVE-2026-63888 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63888

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
======================================================================

CVE-2026-63888	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-126;CWE-415;*CWE-416;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'An iSCSI target Text PDU handling bug can read 4 bytes past the allocated text_in buffer during DataDigest CRC calculation and can also leave cmd text_in_ptr pointing to freed memory after an ERL 1 or higher bad DataDigest drop. A remote initiator can trigger the dangerous path by using a Text PDU sequence with DataDigest enabled and a bad CRC, after which a later Text Request on the same ITT or command release can free the same buffer again. For the CVSS the PR:N is used for the paranoid score because an attacker may only need network access to an exposed iSCSI target that allows login or accepts the attacker as an initiator. The base scenario is still constrained by iSCSI target exposure, negotiated DataDigest, ERL 1 or higher behavior, and timing or state reuse requirements. Impact is at least remote denial of service via kernel crash. In worst case the double-free may allow confidentiality and integrity impact due to slab freelist corruption on less hardened kernels and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 9)	YES	WRITE OOB UAF KPANIC 	NO	NO	checked

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

ActionableScore=9
ActionableScoreLower=7

## 1. ActionableScore

* Conservative score: 7
* Paranoid score: 9
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. The affected path is the iSCSI target Text PDU handling path and can be reached by a remote initiator after connection/login conditions.
* Memory corruption, strong corruption primitive: +2. The stale `cmd->text_in_ptr` can be freed twice, producing a double-free.
* Real lifetime corruption: +1. The bug leaves a pointer to freed memory in command state and later cleanup paths can reuse it.
* Reliable kernel crash / strong DoS: +1. The commit states that hardened slab configurations turn the double-free into a remote kernel BUG.
* Important filesystem/storage path: +1. This is in the SCSI target iSCSI storage stack.
* Special protocol conditions: -1. Reliable triggering depends on negotiated `DataDigest`, ERL greater than 0, and a specific Text PDU sequence.

Conservative total: 7

Paranoid additions:

* Confidentiality impact plausible: +1. On non-hardened kernels, slab freelist corruption from a remote double-free can plausibly lead beyond pure crash behavior.
* Integrity impact plausible: +1. The same double-free primitive may corrupt allocator metadata and should be treated as potentially exploitable until manually ruled out.

Paranoid total: 9

## 3. Reachability analysis

A remote iSCSI initiator can reach the vulnerable code path if the target service is exposed and permits the initiator to establish the required session state. The strongest path requires `DataDigest=CRC32C`, ERL greater than 0, a bad DataDigest drop, and either a later Text Request on the same ITT or command teardown. This is not a local namespace or container-only issue. It is network-facing in deployments exposing LIO iSCSI targets, although iSCSI is commonly restricted to storage or data-center networks rather than the public Internet.

## 4. Severity interpretation

This is stronger than an ordinary Moderate issue because the patch fixes both a KASAN-confirmed 4-byte OOB read and a remote double-free. The OOB read alone looks limited because the bytes feed CRC calculation and are not directly returned to the attacker. The double-free is the decisive issue: realistic hardened systems may crash, while non-hardened systems may experience slab freelist corruption. Practical privilege escalation or code execution is not demonstrated, but the remote lifetime corruption primitive is important enough to require manual review.

## 5. One-sentence report phrase

A remote iSCSI initiator can trigger a Text PDU DataDigest handling flaw that causes a 4 byte CRC overread and a stale pointer double-free, leading to remote kernel crash and possible allocator corruption on less hardened kernels.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Remote reachable double-free in a storage target protocol should not be auto-closed, especially because the commit explicitly distinguishes hardened-kernel BUG behavior from non-hardened slab freelist corruption.

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

Patch: scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd() [ Upstream
Commit: f7948af0dd03de84079dcd4dc215a69fd6fbb95d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f7948af0dd03de84079dcd4dc215a69fd6fbb95d

Changed files:
  drivers/target/iscsi/iscsi_target.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=f7948af0dd03de84079dcd4dc215a69fd6fbb95d

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

The original Linux kernel CVE announcement for CVE-2026-63888 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63888

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:L/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: 7
  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).