# CVE-2026-89558: md/raid10: fix still_degraded being inverted in raid10_sync_request()

> A logic error in Linux kernel RAID10 recovery causes silent data corruption when re-adding disks to a degraded array.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-89558, DEBIAN-CVE-2026-89558, GHSA-6w6j-fmcg-fgj3, UBUNTU-CVE-2026-89558

## What is CVE-2026-89558?

CVE-2026-89558 is a critical vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

md/raid10: fix still_degraded being inverted in raid10_sync_request()

Commit fe6a19d40ceb ("md/md-bitmap: merge md_bitmap_start_sync() into
bitmap_operations") converted still_degraded from int to bool, but
inverted the assignment in the loop that checks whether the array will
still be degraded after the current device is recovered:
"still_degraded = 1" became "still_degraded = false".

As a result, recovering a device while another mirror is still missing
calls md_bitmap_start_sync() with degraded == false, which clears bitmap
bits that the still-missing device needs.  When that device is re-added,
its bitmap-based recovery finds the bits already cleared and skips every
region written while the array was degraded, so it is marked In_sync
while holding stale data: silent corruption.

Reproducer (raid10 near=2, 4 disks, internal bitmap):
 - fail and remove one disk of each mirror pair
 - write to the degraded array
 - re-add both disks and let recovery finish
 - "check" reports mismatch_cnt=262272 after 256 MiB of degraded
   writes and file contents differ; the second disk's "recovery"
   completes in milliseconds because everything is skipped

The same conversion in raid1 got it right (still_degraded = true).
Restore the correct value.

## Which versions are affected by CVE-2026-89558?


## How do I fix CVE-2026-89558?

Apply the vendor's patch.

## Is CVE-2026-89558 being exploited?

There is no known exploitation of CVE-2026-89558 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89558 and fix it if it is affected.

What it is: CVE-2026-89558 is a critical vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89558 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-2026-89558/ (Markdown: https://insights.sbomify.com/CVE-2026-89558/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89558
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89558
- OSV: https://osv.dev/vulnerability/CVE-2026-89558

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89558/
Summaries are generated and may contain mistakes; the official description above is the record.