[CVE-2026-89607][IMPORTANT] ecryptfs: reject oversized encrypted_key_size in parse_tag_3_packet

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

CVE: CVE-2026-89607
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: ecryptfs: reject oversized encrypted_key_size in parse_tag_3_packet
Commit: ccd13eff0e7356d2aa28b127b577e4e5ad4563f5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ccd13eff0e7356d2aa28b127b577e4e5ad4563f5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89607
Analysis date: Sat, 12 Sep 2026 06:59:34 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89607 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89607

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-2026-89607	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-89607 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;*CWE-20;CWE-120;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'An out of bounds write in the eCryptfs passphrase key handling path occurs because parse_tag_3_packet can accept an encrypted_key_size larger than ECRYPTFS_MAX_KEY_BYTES. The value is later reused as decrypted_key_size, so crypto_skcipher_decrypt can write past decrypted_key and memcpy can write past crypt_stat key, corrupting adjacent eCryptfs kernel structures. A local attacker who can cause the kernel to parse crafted eCryptfs Tag 3 metadata may trigger kernel memory corruption. For the CVSS the PR:L value is used because reliable triggering requires local user or process access to the eCryptfs parsing path, not full administrator privileges in all practical deployments. The issue is not directly network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow privilege escalation due to kernel out of bounds writes.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7)  SKIP CVE-2026-89607 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	WRITE OOB DISK LINUS KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	-	-	checked

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

ActionableScore=7
ActionableScoreLower=6
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 6
* Conservative score: 6. No floor or cap applied.
* Raw paranoid score: 7
* Paranoid score: 7. No floor or cap applied.
* Final recommended bucket: **Strong Important candidate**::

2. Signal breakdown

Conservative signals:

* +2 Strong corruption primitive. The patch establishes two concrete kernel out-of-bounds writes caused by accepting encrypted_key_size larger than ECRYPTFS_MAX_KEY_BYTES.
* +1 Reliable kernel crash or strong DoS. Overflowing decrypted_key and crypt_stat key into adjacent eCryptfs structures can realistically corrupt mutexes, lists, and other live kernel state.
* +1 Integrity plausible. The bug writes beyond fixed kernel buffers and corrupts protected kernel data structures, not merely passive metadata.
* +1 Important filesystem/storage path. The bug is in eCryptfs key parsing and affects filesystem encryption metadata handling.
* +1 Attacker-influenced memory layout and size mismatch. The vulnerable size is derived from attacker-controlled Tag 3 packet metadata and is reused across buffers with different limits.

Paranoid additional signal:

* +1 Strong exploitation concern. The OOB writes target adjacent active eCryptfs structures such as ecryptfs_auth_tok and ecryptfs_crypt_stat, so privilege-escalation potential is technically defensible even though no controlled reclaim or arbitrary write primitive is demonstrated.

Non-awarded material signals:

* RealUAF not awarded. This is an OOB write, not a lifetime or stale-reference bug.
* Controlled reclaim not demonstrated.
* Arbitrary kernel read/write not demonstrated.
* Confidentiality not awarded because no disclosure path is established.
* Remote reachability not awarded. This is local filesystem metadata parsing, not a direct network path.
* Concrete repeated release/refcount not applicable.
* Extra availability not awarded beyond the same memory-corruption crash risk.

3. Reachability analysis

The attacker must cause the kernel eCryptfs parser to process crafted Tag 3 passphrase metadata with an oversized encrypted_key_size. The supplied evidence supports a local attacker model, but the complete privilege boundary depends on how eCryptfs mounting or file access is exposed in the target system. Some environments may allow user-accessible eCryptfs workflows, while others may require administrator-controlled mount setup.

Host-admin-equivalent privilege is not positively established by the patch, so HostAdminRequired is UNKNOWN rather than YES. Below-host-admin reachability is plausible but not fully proven from the supplied patch alone, so HostAdminRequired is not set to NO. No namespace-scoped privilege requirement is established. No special hardware, race, or timing condition is required. The issue is not network reachable.

4. Primitive and severity interpretation

The exact primitive is attacker-influenced kernel out-of-bounds write. parse_tag_3_packet accepts a Tag 3 encrypted_key_size up to the larger encrypted_key buffer size, but the passphrase decrypt path later uses the same value as decrypted_key_size for smaller ECRYPTFS_MAX_KEY_BYTES buffers. This allows crypto_skcipher_decrypt to overflow decrypted_key and then memcpy to overflow crypt_stat->key.

This is active kernel structure corruption rather than crash-only invalid input. It is PrimitiveClass CLASS_A because the patch establishes concrete OOB writes into kernel memory with attacker-influenced size and filesystem metadata. The demonstrated consequence is kernel memory corruption and likely DoS. The speculative but defensible consequence is local privilege escalation because adjacent active eCryptfs structures are corrupted, although a complete exploit chain is not shown.

ImportantCandidate is YES because this is a strong kernel memory corruption primitive in filesystem encryption code. AutoDowngradeAllowed is NO because automatic closure would discard a concrete OOB-write primitive with unresolved exploitation leverage.

5. One-sentence report phrase

A local eCryptfs metadata parsing flaw allows an oversized Tag 3 encrypted_key_size to drive out-of-bounds writes in the passphrase key path, corrupting kernel eCryptfs structures and requiring manual review for possible privilege escalation beyond DoS.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Concrete kernel out-of-bounds writes are established, and the corrupted targets are active eCryptfs kernel structures. Even without a demonstrated LPE chain, this is not safe for automatic downgrade.

7. Call-site confidence

Call-site confidence: high

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

Patch: ecryptfs: reject oversized encrypted_key_size in parse_tag_3_packet
Commit: ccd13eff0e7356d2aa28b127b577e4e5ad4563f5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ccd13eff0e7356d2aa28b127b577e4e5ad4563f5

Commit description:

parse_tag_3_packet() set encrypted_key_size from the Tag 3 packet body
without bounding it against ECRYPTFS_MAX_KEY_BYTES (64). When
encrypted_key_size > 64, decrypt_passphrase_encrypted_session_key()
sets decrypted_key_size = encrypted_key_size and performs two
out-of-bounds writes:

1. crypto_skcipher_decrypt() writes encrypted_key_size bytes into
   decrypted_key[64] via scatterlist, overflowing into the parent
   ecryptfs_auth_tok struct.
2. memcpy(crypt_stat->key, decrypted_key, decrypted_key_size) writes
   into crypt_stat->key[64], corrupting root_iv, keysig_list, and
   mutexes in ecryptfs_crypt_stat.

Only AES-192 (cipher code 0x08) enables this because it sets
crypt_stat->key_size = 24 independently of encrypted_key_size,
allowing crypto_skcipher_setkey() to succeed while encrypted_key_size
exceeds ECRYPTFS_MAX_KEY_BYTES.

The PKI decryption path (parse_tag_65_packet) already validates
decrypted_key_size <= ECRYPTFS_MAX_KEY_BYTES; the passphrase path
omits this check.

Bound encrypted_key_size against ECRYPTFS_MAX_KEY_BYTES (64) rather
than ECRYPTFS_MAX_ENCRYPTED_KEY_BYTES (512). The 64-byte limit also
protects the 512-byte encrypted_key[] buffer, so the former 512-byte
check is removed as redundant.

Fixes: 237fead ("[PATCH] ecryptfs: fs/Makefile and fs/Kconfig")
Cc: <stable@vger.kernel.org>
Signed-off-by: HanQuan <eilaimemedsnaimel@gmail.com>
[tyhicks: Adjust the code comment to refer to macros representing the
 buffer sizes rather than mentioning the buffer size values since they
 may change in the future]
Signed-off-by: Tyler Hicks <code@tyhicks.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/ecryptfs/keystore.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=ccd13eff0e7356d2aa28b127b577e4e5ad4563f5

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

The original Linux kernel CVE announcement for CVE-2026-89607 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89607

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:L/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 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).