CVE-2026-45734
MEDIUM
5,3
Source: [email protected]
Attack Vector: network
Attack Complexity: low
Privileges Required: none
User Interaction: none
Scope: unchanged
Confidentiality: none
Integrity: low
Availability: none
Description
AI Translation Available
MyBB is free and open source forum software. Prior to 1.8.40, the built-in CAPTCHA does not consistently enforce single-use semantics, allowing remote attackers to bypass CAPTCHA controls through challenge replay. The successful validation paths in contact.php, member.php?action=do_resendactivation, member.php?action=do_lostpw, member.php?action=do_emailuser, and sendthread.php?action=do_sendtofriend do not call captcha::invalidate_captcha() for the MyBB Default CAPTCHA selected by the captchaimage setting. A valid response can therefore be reused until a non-vulnerable endpoint invalidates it, an incorrect response is submitted, or the challenge expires. This issue is fixed in version 1.8.40.
837
Improper Enforcement of a Single, Unique Action
IncompleteCommon Consequences
Security Scopes Affected:
Other
Potential Impacts:
Varies By Context
Applicable Platforms
Technologies:
Not Technology-Specific, Web Based, Web Server
https://github.com/mybb/mybb/commit/c2ed54f9259b9ce05728a9e657169033fe4adffc
https://github.com/mybb/mybb/releases/tag/mybb_1840
https://github.com/mybb/mybb/security/advisories/GHSA-jrrr-f3jw-mjmc
https://mybb.com/versions/1.8.40