* [CVE-2026-89606][MODERATE 7.0] ecryptfs: reject too-small tag 70 packets
@ 2026-09-12 0:37 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-12 0:37 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89606
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ecryptfs: reject too-small tag 70 packets
Commit: 9d88391bbed76eb091cddd50b0af87b1c6f22589
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d88391bbed76eb091cddd50b0af87b1c6f22589
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89606
Analysis date: Fri, 11 Sep 2026 20:37:42 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: NO
Summary:
A malformed eCryptfs tag 70 filename packet can underflow the encrypted filename size calculation in ecryptfs_parse_tag_70_packet, causing invalid parser behavior and possible local denial of service, with manual review needed for downstream length handling impact.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89606 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89606
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-89606 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89606 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-191;*CWE-20;CWE-125;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '6.6';DESCR 'An integer underflow in ecryptfs_parse_tag_70_packet can occur when a malformed tag 70 filename encryption packet is smaller than the fixed metadata fields. The underflow can produce a very large encrypted filename size and may lead to invalid memory reads, excessive allocation attempts, or a kernel crash when the malformed filename is parsed. For the CVSS the PR:L is used because practical triggering requires a local user or process able to supply or access crafted eCryptfs backing filenames. The issue is not network reachable by itself and depends on local filesystem exposure of eCryptfs encrypted names. Impact is at least local denial of service via parser failure or kernel crash and in worst case may allow limited confidentiality or integrity impact due to the underflowed length handling. YES REQUIRES MANUAL CHECK.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5) SKIP CVE-2026-89606 UNKNOWN SKIP No affected files built, so skip this CVE NO - - unknown MAYBE OOB DISK SIMPLEFIX LINUS KPANIC PACKET - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=NO
## 1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate**::
No floor or cap changed the conservative score.
No floor or cap changed the paranoid score.
## 2. Signal breakdown
Conservative signals:
* +1 Weak / indirect corruption candidate: the malformed tag 70 packet can underflow a `size_t` filename size calculation and produce a bogus large length.
* +1 Memory layout invariant restoration: the fix restores the required minimum packet layout before subtracting fixed metadata fields.
* +1 Local attacker-controlled parser input: a local user or process with access to crafted eCryptfs backing filenames can plausibly trigger parsing of malformed encrypted filename metadata.
* +1 Reliable DoS / strong availability concern: the underflowed length may lead to invalid reads, excessive allocation attempts, parser failure, or kernel crash.
Paranoid additional signal:
* +1 Unresolved kernel parser impact: the underflowed length is used in filename parsing/decryption logic, and full downstream consequences are not visible from this small patch. This supports manual review sensitivity but does not prove arbitrary write or LPE.
Non-awarded signals:
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Real UAF not demonstrated.
* Concrete repeated release/refcount mutation not present.
* Confidentiality impact not awarded because no user-visible kernel disclosure path is established.
* Integrity impact not awarded because no unauthorized write or protected-object modification is established.
* Remote reachability not established.
* Extra Availability not awarded beyond the same crash/resource failure path.
* ImportantCandidate not set because the patch supports an integer-underflow parser bug, not a strong memory-corruption or security-boundary primitive.
## 3. Reachability analysis
The trigger is local filesystem/parser reachability. A crafted eCryptfs tag 70 filename packet must be supplied or encountered so that `ecryptfs_parse_tag_70_packet()` parses it.
Host-admin-equivalent privilege is not positively required by the supplied context. The practical attacker model is a local user or local process able to place or access malformed eCryptfs encrypted filenames in a relevant backing directory or filesystem image. This is below host-admin in plausible deployments, so `HostAdminRequired=NO`.
No direct network path is shown. Namespace-scoped privilege is not central to this issue and the supplied evidence does not establish a namespace-specific complete trigger chain, so `NamespaceScopedPrivilege=UNKNOWN`.
No race is involved. No special hardware is involved. Prior setup may include an eCryptfs mount or an existing eCryptfs-backed directory, but the vulnerable operation itself is parser-side handling of malformed filename metadata.
## 4. Primitive and severity interpretation
The exact primitive is an integer underflow in `ecryptfs_parse_tag_70_packet()` when `parsed_tag_70_packet_size` is smaller than the fixed tag 70 metadata fields. The resulting `block_aligned_filename_size` may become a very large `size_t` value.
This is not a UAF and not a repeated lifetime/refcount mutation. It is also not a demonstrated arbitrary read/write primitive. The established class is malformed input leading to invalid size computation in a kernel filesystem parser, with likely consequences in the DoS / invalid-read / excessive-allocation range.
PrimitiveClass is `CLASS_C` because the demonstrated behavior is primarily invalid-state and DoS-oriented, without an independently useful corruption primitive. The paranoid score keeps the issue actionable because integer underflow in filesystem parser length handling can have non-obvious downstream effects and should not be automatically closed from the small patch alone.
ImportantCandidate is `NO` because no strong exploitation leverage, ownership/COW bypass, authorization bypass, UAF, arbitrary write, or LPE path is established.
AutoDowngradeAllowed is `NO` because the underflowed length is a concrete kernel parser primitive with unresolved downstream effects and should receive manual review before closure.
Likely operational severity: Actionable Moderate.
## 5. One-sentence report phrase
A malformed eCryptfs tag 70 filename packet can underflow the encrypted filename size calculation in ecryptfs_parse_tag_70_packet, causing invalid parser behavior and possible local denial of service, with manual review needed for downstream length handling impact.
## 6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: the patch fixes a concrete integer underflow in kernel filesystem parser length handling, and the downstream impact of the underflowed filename size is not fully visible from the supplied diff.
## 7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ecryptfs: reject too-small tag 70 packets
Commit: 9d88391bbed76eb091cddd50b0af87b1c6f22589
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d88391bbed76eb091cddd50b0af87b1c6f22589
Commit description:
ecryptfs_parse_tag_70_packet() subtracts fixed metadata fields from the
parsed packet body size to derive the encrypted filename size. A
malformed packet with a body smaller than those fixed fields can underflow
that size calculation.
Reject tag 70 packets before the subtraction unless the body contains the
signature, cipher code, and at least one byte of encrypted filename data.
Fixes: 9c79f34 ("eCryptfs: Filename Encryption: Tag 70 packets")
Cc: <[email protected]>
Signed-off-by: Yichong Chen <[email protected]>
Signed-off-by: Tyler Hicks <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
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=9d88391bbed76eb091cddd50b0af87b1c6f22589
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89606 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89606
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:N/A:H
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS score: 6.6
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: 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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
^ permalink raw reply [relevance 21%]
Results 1-1 of 1 | reverse | sort options + mbox downloads above
-- links below jump to the message on this page --
2026-09-12 0:37 21% [CVE-2026-89606][MODERATE 7.0] ecryptfs: reject too-small tag 70 packets AL-KERNEL
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox