* [CVE-2026-80892][LOW] erofs: cap LZMA stream pool size [ Upstream
@ 2026-09-04 22:13 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-04 22:13 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80892
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: erofs: cap LZMA stream pool size [ Upstream
Commit: 682cb3ece37fc5141e73bc726ccf4adb833e5189
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=682cb3ece37fc5141e73bc726ccf4adb833e5189
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80892
Analysis date: Fri, 04 Sep 2026 18:13:49 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO
Summary:
An EROFS image using LZMA can cause excessive vmalloc memory pinning because the default MicroLZMA stream pool previously scaled with the number of possible CPUs, but exploitation requires a path that causes the system to mount such an image and the impact is resource exhaustion DoS only.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80892 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80892
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: LOW
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-2026-80892 LOW https://www.kernelcve.org/list/?q=CVE-2026-80892 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:N/I:N/A:H';**CWE-400;CWE-770;CWE-789;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'EROFS LZMA decompression can allocate one MicroLZMA stream per possible CPU when the lzma_streams module parameter is unset. Each stream can hold an image supplied dictionary up to 8 MiB, so a small mounted image on a high CPU system can pin a large amount of vmalloc backed memory until the EROFS state is released. For the CVSS the PR:L is used in the paranoid score because some environments may let a local low privileged user supply filesystem images to a mount helper, container runtime, or delegated storage service even though direct mounting is normally administrative. The issue is not network reachable by itself and requires a local path that causes the target system to mount an EROFS image. Impact is denial of service through memory pressure or resource exhaustion. No memory corruption, information disclosure, or privilege escalation primitive is evident from the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) YES DISK SIMPLEFIX HARDWARE LINUS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked
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ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
ActionableScoreLower=1
## 1. ActionableScore
* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::
## 2. Signal breakdown
Triggered signals:
* Availability impact realistic: +1
The mounted EROFS image can pin vmalloc backed LZMA dictionary memory, causing memory pressure or resource exhaustion.
* Important filesystem/storage path: +1 in paranoid scoring only
EROFS is a filesystem mount path, but the issue affects decompressor resource sizing rather than metadata integrity, page cache ownership, or persistent filesystem corruption.
* Local low privileged trigger: +1 in paranoid scoring only
Direct mounting normally requires CAP_SYS_ADMIN, but some environments may allow a low privileged local user to provide filesystem images to a mount helper, container runtime, sandbox, or storage service.
Subtracted signals:
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2 for conservative scoring
A normal local user cannot directly mount arbitrary EROFS images on standard systems.
* Rare or configuration dependent exposure: -1
The issue requires EROFS with LZMA support and a system that mounts attacker supplied or unexpected EROFS images, preferably on a high CPU count system.
Not triggered:
* No generic memory corruption.
The patch only caps allocation scaling and does not show UAF, OOB write, double free, type confusion, arbitrary write, or stale pointer use.
* No privilege escalation plausible.
The primitive is memory pinning/resource exhaustion only.
* No confidentiality or integrity impact.
The patch does not indicate information disclosure, unauthorized writes, page cache corruption, CoW bypass, or filesystem metadata corruption.
* No remote reachable signal.
The vulnerable path is mount driven and not network reachable by itself.
## 3. Reachability analysis
The realistic trigger is local and depends on causing the target system to mount an EROFS image using LZMA compression. In ordinary deployments this requires administrative mount privileges, so the conservative interpretation treats it as PR:H equivalent for practical triggering. A paranoid interpretation uses PR:L style reachability only for environments where untrusted users can submit filesystem images to an automount service, container runtime, sandbox, VM image pipeline, or similar delegated mounting workflow.
The path is not directly network triggered. Public Internet exposure is not expected unless a network service accepts untrusted images and mounts them locally. The issue is more relevant on high CPU count systems because the previous default stream count scaled with num_possible_cpus(), allowing up to 8 MiB per stream.
## 4. Severity interpretation
This behaves like a resource exhaustion bug, not a memory corruption vulnerability. The practical impact is DoS through vmalloc memory pressure after mounting a crafted or unexpectedly expensive EROFS image. There is no supported path to privilege escalation, kernel memory corruption, sensitive data exposure, or persistent filesystem integrity damage.
Conservative severity is Low-like to ordinary Moderate because normal triggering requires CAP_SYS_ADMIN and the bug is configuration dependent. Paranoid severity remains below Actionable Moderate because even with delegated image mounting the primitive is still resource exhaustion only.
## 5. One-sentence report phrase
An EROFS image using LZMA can cause excessive vmalloc memory pinning because the default MicroLZMA stream pool previously scaled with the number of possible CPUs, but exploitation requires a path that causes the system to mount such an image and the impact is resource exhaustion DoS only.
## 6. Manual review recommendation
NO MANUAL CHECK NEEDED
This is a bounded resource exhaustion issue with no evidence of UAF, OOB access, arbitrary write, page cache corruption, permission bypass, or privilege escalation. It can be handled as non-urgent unless the product commonly mounts untrusted EROFS images on high CPU count systems.
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: erofs: cap LZMA stream pool size [ Upstream
Commit: 682cb3ece37fc5141e73bc726ccf4adb833e5189
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=682cb3ece37fc5141e73bc726ccf4adb833e5189
Changed files:
fs/erofs/decompressor_lzma.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=682cb3ece37fc5141e73bc726ccf4adb833e5189
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80892 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80892
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:H/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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: 1
Paranoid ActionableScore: 2
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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).
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