# CVE-2026-12939: Newsletters <= 4.15 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'link' Shortcode Attribute

> Authenticated contributors can inject arbitrary scripts via the link shortcode attribute, leading to stored XSS execution for other users.

- **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:** 29 Jul 2026
- **Updated:** 29 Jul 2026
- **Also known as:** GHSA-x3c9-qfw8-8r9c

## What is CVE-2026-12939?

CVE-2026-12939 is a medium-severity cross-site scripting vulnerability in contrid Newsletters, published on 29 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

The Newsletters Lite plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'link' attribute of the post_thumbnail (and newsletters_post_thumbnail) shortcodes in versions up to and including 4.15. This is due to insufficient input sanitization and output escaping in the post_thumbnail() method in helpers/shortcode.php, which concatenates the user-controlled $link shortcode attribute directly into an href attribute without esc_url() or esc_attr(). 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.

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

## Which versions are affected by CVE-2026-12939?


## How do I fix CVE-2026-12939?

No fix has been published for CVE-2026-12939 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-12939 being exploited?

There is no known exploitation of CVE-2026-12939 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-12939 and fix it if it is affected.

What it is: CVE-2026-12939 is a medium-severity cross-site scripting vulnerability in contrid Newsletters, published on 29 Jul 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-2026-12939 in the wild and no public exploit code.

Affected product: contrid Newsletters. 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-2026-12939/ (Markdown: https://insights.sbomify.com/CVE-2026-12939/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-12939
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-12939
- OSV: https://osv.dev/vulnerability/CVE-2026-12939

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-12939/
Summaries are generated and may contain mistakes; the official description above is the record.