# CVE-2026-104021: Code injection in Fastcache by Host.it

> Authenticated administrators can inject arbitrary Apache directives into .htaccess to execute remote PHP code on the server.

- **Severity:** High 7.2 (`CVSS:3.1/AV:N/AC:L/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:** 10 Oct 2026
- **Updated:** 11 Oct 2026
- **Also known as:** GHSA-hm53-mjmf-w6v4

## What is CVE-2026-104021?

CVE-2026-104021 is a high-severity code injection vulnerability in hostspa Fastcache by Host.it, published on 10 Oct 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

The Fastcache by Host.it plugin for WordPress is vulnerable to Code Injection in all versions up to, and including, 1.7.4 via the `fastcache_settings[cache_cookie_exclude][]` parameter. This is due to the plugin registering the `cache_cookie_exclude` setting via `register_setting()` without a `sanitize_callback`, while `buildSiteHtaccessRules()` applies only `trim()` to each cookie value before interpolating it directly into an Apache `RewriteCond` line — a normalization that strips surrounding whitespace but leaves embedded newlines intact, allowing an attacker to break out of the capture group and append arbitrary directives. This makes it possible for authenticated attackers, with administrator-level access and above, to inject arbitrary Apache directives into the site's `.htaccess` file via `file_put_contents()`, enabling server-level configuration changes such as setting `php_value auto_prepend_file` to execute attacker-controlled PHP code on every request.

Weakness: CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-104021?


## How do I fix CVE-2026-104021?

No fix has been published for CVE-2026-104021 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-104021 being exploited?

There is no known exploitation of CVE-2026-104021 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-104021 and fix it if it is affected.

What it is: CVE-2026-104021 is a high-severity code injection vulnerability in hostspa Fastcache by Host.it, published on 10 Oct 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-104021 in the wild and no public exploit code.

Affected product: hostspa Fastcache by Host.it. 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-2026-104021/ (Markdown: https://insights.sbomify.com/CVE-2026-104021/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-104021
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-104021
- OSV: https://osv.dev/vulnerability/CVE-2026-104021

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-104021/
Summaries are generated and may contain mistakes; the official description above is the record.