# CVE-2026-45122: MyBB: Insufficient permission check for calendar event move

> Attackers with source calendar moderation rights can move events to calendars where they lack moderation permissions, bypassing access controls.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/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:** 18 Aug 2026
- **Updated:** 18 Aug 2026
- **Also known as:** GHSA-839m-gpw8-59j4

## What is CVE-2026-45122?

CVE-2026-45122 is a medium-severity missing authorization vulnerability in mybb, published on 18 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

MyBB is free and open source forum software. Prior to 1.8.40, the calendar module does not validate moderation permissions for the destination calendar when moving events. A user with moderation permission for the source calendar can move an event to a calendar where the user has only viewing permission because the do_move action in calendar.php does not check canmoderateevents for the target calendar. The uniquely identifying implementation details include calendar event move, source calendar moderation permission, and destination calendar viewing permission. This issue is fixed in version 1.8.40.

Weakness: CWE-863 (Incorrect Authorization)

## Which versions are affected by CVE-2026-45122?


## How do I fix CVE-2026-45122?

No fix has been published for CVE-2026-45122 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-45122 being exploited?

There is no known exploitation of CVE-2026-45122 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45122 and fix it if it is affected.

What it is: CVE-2026-45122 is a medium-severity missing authorization vulnerability in mybb, published on 18 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-2026-45122 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-2026-45122/ (Markdown: https://insights.sbomify.com/CVE-2026-45122/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45122
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45122
- OSV: https://osv.dev/vulnerability/CVE-2026-45122

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45122/
Summaries are generated and may contain mistakes; the official description above is the record.