# CVE-2026-45118: MyBB: Contact page reflected XSS

> Attackers can inject JavaScript via the contact page redirect parameter, allowing script execution when victims click a link.

- **Severity:** Critical 9.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 18 Aug 2026
- **Updated:** 18 Aug 2026
- **Also known as:** GHSA-wf92-5q5h-qr53

## What is CVE-2026-45118?

CVE-2026-45118 is a critical cross-site scripting vulnerability in mybb, published on 18 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

MyBB is free and open source forum software. Prior to 1.8.40, the Contact module does not validate a redirect URL or protocol correctly, resulting in an open redirect and reflected JavaScript code injection. contact.php accepts the redirect target from the from HTTP parameter in $mybb->input['from'] or the Referer HTTP header in $_SERVER['HTTP_REFERER'] and passes it to redirect() without sufficient verification. A javascript: URI becomes the target of the `Click here if you don't want to wait any longer` link because $force_redirect is true, allowing script execution when a victim selects the link. This issue is fixed in version 1.8.40.

Weakness: CWE-83 (Improper Neutralization of Script in Attributes in a Web Page)

## Which versions are affected by CVE-2026-45118?


## How do I fix CVE-2026-45118?

No fix has been published for CVE-2026-45118 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-45118 being exploited?

There is no known exploitation of CVE-2026-45118 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45118 and fix it if it is affected.

What it is: CVE-2026-45118 is a critical cross-site scripting vulnerability in mybb, published on 18 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-45118 in the wild and no public exploit code.

Affected product: mybb. 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-2026-45118/ (Markdown: https://insights.sbomify.com/CVE-2026-45118/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45118
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45118
- OSV: https://osv.dev/vulnerability/CVE-2026-45118

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45118/
Summaries are generated and may contain mistakes; the official description above is the record.