# CVE-2026-15421: Speed Optimizer <= 7.8.0 - Authenticated (Contributor+) Stored Cross-Site Scripting via Image Tag Attributes

> Authenticated contributors can inject arbitrary scripts via image tags in Speed Optimizer plugin when Lazy Load Media is enabled.

- **Severity:** Medium 6.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 19 Aug 2026
- **Updated:** 20 Aug 2026
- **Also known as:** GHSA-8r64-rxjj-mp32

## What is CVE-2026-15421?

CVE-2026-15421 is a medium-severity cross-site scripting vulnerability in siteground Speed Optimizer – The All-In-One Performance-Boosting Plugin, published on 19 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

The Speed Optimizer – The All-In-One Performance-Boosting Plugin plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Image Tag Attributes in all versions up to, and including, 7.8.0 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This is only exploitable when the site administrator has enabled the Lazy Load Media option in the plugin settings.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-15421?


## How do I fix CVE-2026-15421?

No fix has been published for CVE-2026-15421 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-15421 being exploited?

There is no known exploitation of CVE-2026-15421 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-15421 and fix it if it is affected.

What it is: CVE-2026-15421 is a medium-severity cross-site scripting vulnerability in siteground Speed Optimizer – The All-In-One Performance-Boosting Plugin, published on 19 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-15421 in the wild and no public exploit code.

Affected product: siteground Speed Optimizer – The All-In-One Performance-Boosting Plugin. 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-2026-15421/ (Markdown: https://insights.sbomify.com/CVE-2026-15421/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-15421
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-15421
- OSV: https://osv.dev/vulnerability/CVE-2026-15421

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-15421/
Summaries are generated and may contain mistakes; the official description above is the record.