# CVE-2026-10821: Yoast SEO Premium < 27.6.1 - Author+ Arbitrary .htaccess Directive Injection to RCE

> Authors can inject Apache directives into .htaccess to achieve remote code execution via chained media uploads in Yoast SEO Premium.

- **Severity:** Medium 6.6 (`CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 2 Sep 2026
- **Updated:** 2 Sep 2026
- **Also known as:** GHSA-2r8j-r49x-m28r

## What is CVE-2026-10821?

CVE-2026-10821 is a medium-severity code injection vulnerability in Unknown Yoast SEO Premium, published on 2 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

The Yoast SEO Premium WordPress plugin before 27.6.1 does not sanitize control characters from redirect origins before writing them to the site's Apache configuration file when the file-based redirect mode is enabled, and the redirect-creation endpoint is reachable by users with only Author-level access. This allows such users to inject arbitrary newline-delimited Apache directives into the root .htaccess file. On Apache servers that honour PHP directives, the injection can be chained with the user's own media upload (a polyglot image carrying a PHP payload) and an auto_prepend_file directive to achieve Remote Code Execution.

Weakness: CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component)

## Which versions are affected by CVE-2026-10821?


## How do I fix CVE-2026-10821?

No fix has been published for CVE-2026-10821 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-10821 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-10821 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-10821 and fix it if it is affected.

What it is: CVE-2026-10821 is a medium-severity code injection vulnerability in Unknown Yoast SEO Premium, published on 2 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-10821 exists.

Affected product: Unknown Yoast SEO Premium. 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-2026-10821/ (Markdown: https://insights.sbomify.com/CVE-2026-10821/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-10821
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-10821
- OSV: https://osv.dev/vulnerability/CVE-2026-10821

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-10821/
Summaries are generated and may contain mistakes; the official description above is the record.