# CVE-2026-74591: mm/filemap: __filemap_add_folio() restore index before retrying

> A race condition in the Linux kernel's filemap handling can cause memory corruption, leading to system crashes or potential code execution.

- **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:** 22 Aug 2026
- **Updated:** 25 Aug 2026
- **Also known as:** BELL-CVE-2026-74591, DEBIAN-CVE-2026-74591, GHSA-xwx5-8c6h-6c7v, UBUNTU-CVE-2026-74591

## What is CVE-2026-74591?

CVE-2026-74591 is a critical vulnerability in Linux, published on 22 Aug 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:

mm/filemap: __filemap_add_folio() restore index before retrying

In __filemap_add_folio()'s split-a-conflict loop, xas_set_order() is
applied repeatedly: each application modifies xas.xa_index, rounding it
down according to the split_order attempted at that stage: and if all goes
as intended, it eventually (or immediately) converges on an
xas_try_split() to the required folio_order, with xas.xa_index now the
same as index: then xas_store() puts the new folio into the xarray there.

But if a new node was needed, and GFP_NOWAIT allocation did not get one,
the lock is dropped, xas_nomem() used to allocate, and sequence retried. 
If (that part of) the xarray is unchanged when the lock is reacquired, no
problem.  But what if the conflict was meanwhile resolved by another
thread (perhaps even doing the same thing, inserting a folio at that same
index)?  Isn't there a danger of now putting our folio into the xarray at
an intermediate rounded-down index?  With !folio_contains() bug to follow,
when CONFIG_DEBUG_VM=y is checking for that.

Fix this with an xas_set_order() to restore the original xas.xa_index at
the bottom of the loop, so the retry does a full re-evaluation after
reacquiring the lock, and cannot reach xas_store() with the wrong index.

Production was suffering from rare SIGILLs and SIGSEGVs, executable text
found a page away from where it belonged, !folio_contains() bug hit when
debug enabled: symptoms not seen since this patch went in.

## Which versions are affected by CVE-2026-74591?


## How do I fix CVE-2026-74591?

Apply the vendor's patch.

## Is CVE-2026-74591 being exploited?

There is no known exploitation of CVE-2026-74591 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74591 and fix it if it is affected.

What it is: CVE-2026-74591 is a critical vulnerability in Linux, published on 22 Aug 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-2026-74591 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-2026-74591/ (Markdown: https://insights.sbomify.com/CVE-2026-74591/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74591
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74591
- OSV: https://osv.dev/vulnerability/CVE-2026-74591

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74591/
Summaries are generated and may contain mistakes; the official description above is the record.