# CVE-2026-46482

## Summary

- **CVE ID:** CVE-2026-46482
- **Severity:** MEDIUM
- **CVSS Score:** 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N)
- **CWE:** CWE-636
- **Published:** Aug 18, 2026
- **Last Modified:** Aug 18, 2026

## Description

### Impact
The registration component does not validate the text-based _Security Question_ CAPTCHA correctly, allowing attackers to bypass the challenge via a specially crafted value.


[CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N](https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N)

### Details
The public _Registration_ workflow ([`member.php?action=do_register`](https://github.com/mybb/mybb/blob/mybb_1839/member.php#L262-L307)) accepts a hidden field `question_id` — expected to match the question session identifier (`mybb_questionsessions.sid`) — and validates the challenge answer without a fail-closed fallback for invalid identifiers. If the value is blank, forged, or expired, the request continues without a question-related error.

### Patches
MyBB 1.8.(...) resolves this issue with the following changes:

- Commit: https://github.com/mybb/mybb/commit/
  - `.patch`: https://github.com/mybb/mybb/commit/.patch

### References
- Release Notes: https://mybb.com/versions/1.8.(...)/

### For more information
Go to [mybb.com/security](https://mybb.com/security/) to report possible security concerns or to learn more about security research at MyBB.

### Contact
The security team can be reached at [security@mybb.com](mailto:security@mybb.com).

## Affected Products

- mybb — mybb (< 1.8.40)

## References

- [CNA](https://github.com/mybb/mybb/security/advisories/GHSA-v2h7-4jp7-j6hh)
- [CNA](https://github.com/mybb/mybb/commit/bd2a3447939d3084a5926dd66ece04649e0e0d60)
- [CNA](https://github.com/mybb/mybb/releases/tag/mybb_1840)
- [CNA](https://mybb.com/versions/1.8.40)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.33%
- **EPSS Percentile:** 25.7

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._