# CVE-2026-98067: erofs: disable LZ4 rolling decompression for now

> A flaw in Linux kernel EROFS LZ4 rolling decompression causes memory corruption due to unsafe backward copying, potentially leading to data leaks or system crashes.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-104828, BELL-CVE-2026-98067, DEBIAN-CVE-2026-98067, GHSA-37cq-5ff4-fh64, UBUNTU-CVE-2026-98067

## What is CVE-2026-98067?

CVE-2026-98067 is a memory corruption vulnerability in Linux, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

erofs: disable LZ4 rolling decompression for now

LZ4 rolling decompression [1] was introduced to reduce the memory
footprint of temporary pages:

 For many cases, it is needed for users to read small data within
 a compressed extent (pcluster), either due to random small read, or
 since uptodate folios (typically order-0) cannot be reused for
 decompression again since decompression algorithm refills
 already-uptodate folios.

Rolling decompression works because LZ4 is LZ77-based and only refers
to the most recent 64 KiB of decompressed data, so in theory only a
bounded rolling window of temporary pages is needed when decompressing.

It can save a lot of temporary memory, e.g.
 601,960-byte data can be compressed into a 256k LZ4 compressed extent,
 which means it needs 146 extra pages per request in the worst case if
 rolling decompression is disabled.

However, the upstream LZ4 implementation is not under EROFS' control:
For example, the literal copy memmove() may still **copy long literals
backward** on x86 based on the address comparison even when the source
and destination ranges do not overlap (IOWs, inline decompression
doesn't need to be considered here). That breaks the rolling assumption
and makes the optimization broken.

Disable it for now to make sure the data correctness first since EROFS
is used everywhere now: The rolling window approach can be revived once
we either ensure that the official LZ4 code always copies forward for
non-overlapping ranges or maintain our own LZ4 implementation in EROFS.

The main impact is a higher runtime memory footprint; However, recent
commit 0f6273ab4637 ("erofs: add a reserved buffer pool for lz4
decompression") helps mitigate this when enabled but it's still not
perfect.

[1] https://www.usenix.org/conference/atc19/presentation/gao
    § 3.3 Decompression

## Which versions are affected by CVE-2026-98067?


## How do I fix CVE-2026-98067?

Apply the vendor's patch.

## Is CVE-2026-98067 being exploited?

There is no known exploitation of CVE-2026-98067 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98067 and fix it if it is affected.

What it is: CVE-2026-98067 is a memory corruption vulnerability in Linux, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98067 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98067/ (Markdown: https://insights.sbomify.com/CVE-2026-98067/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98067
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98067
- OSV: https://osv.dev/vulnerability/CVE-2026-98067

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98067/
Summaries are generated and may contain mistakes; the official description above is the record.