5.3

CVE-2026-46482

MyBB: Security Question insufficient validation

### 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).
Daten sind bereitgestellt durch das CVE Programm von einer CVE Numbering Authority (CNA) (Unstrukturiert).
Herstellermybb
≫
Produkt mybb
Version < 1.8.40
Status affected
VulnDex Vulnerability Enrichment
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Zu dieser CVE wurde keine Warnung gefunden.
EPSS Metriken
Typ Quelle Score Percentile
EPSS FIRST.org 0.33% 0.258
CVSS Metriken
Quelle Base Score Exploit Score Impact Score Vector String
security-advisories@github.com 5.3 3.9 1.4
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
CWE-636 Not Failing Securely ('Failing Open')

When the product encounters an error condition or failure, its design requires it to fall back to a state that is less secure than other options that are available, such as selecting the weakest encryption algorithm or using the most permissive access control restrictions.

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