{"id":"CVE-2026-45734","state":"PUBLISHED","title":"MyBB: Default CAPTCHA missing invalidation","description":"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.","publishedAt":"2026-08-18T15:51:07.257Z","updatedAt":"2026-08-19T14:43:38.996Z","severity":{"score":5.3,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["mybb mybb"],"affected":[{"vendor":"mybb","product":"mybb","versions":[{"version":"< 1.8.40","status":"affected"}]}],"references":["https://github.com/mybb/mybb/security/advisories/GHSA-jrrr-f3jw-mjmc","https://github.com/mybb/mybb/commit/c2ed54f9259b9ce05728a9e657169033fe4adffc","https://github.com/mybb/mybb/releases/tag/mybb_1840","https://mybb.com/versions/1.8.40"],"weaknesses":["CWE-837"],"ingestedAt":"2026-10-29T20:12:07.131Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/45xxx/CVE-2026-45734.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-45734","state":"PUBLISHED","datePublished":"2026-08-18T15:51:07.257Z","dateUpdated":"2026-08-19T14:43:38.996Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-05-13T05:51:48.667Z"},"containers":{"cna":{"title":"MyBB: Default CAPTCHA missing invalidation","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"mybb","product":"mybb","versions":[{"version":"< 1.8.40","status":"affected"}]}],"references":[{"url":"https://github.com/mybb/mybb/security/advisories/GHSA-jrrr-f3jw-mjmc","name":"https://github.com/mybb/mybb/security/advisories/GHSA-jrrr-f3jw-mjmc","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/mybb/mybb/commit/c2ed54f9259b9ce05728a9e657169033fe4adffc","name":"https://github.com/mybb/mybb/commit/c2ed54f9259b9ce05728a9e657169033fe4adffc","tags":["x_refsource_MISC"]},{"url":"https://github.com/mybb/mybb/releases/tag/mybb_1840","name":"https://github.com/mybb/mybb/releases/tag/mybb_1840","tags":["x_refsource_MISC"]},{"url":"https://mybb.com/versions/1.8.40","name":"https://mybb.com/versions/1.8.40","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":5.3,"baseSeverity":"MEDIUM","confidentialityImpact":"NONE","integrityImpact":"LOW","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-837","lang":"en","description":"CWE-837: Improper Enforcement of a Single, Unique Action","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-08-18T15:51:07.257Z"},"source":{"advisory":"GHSA-jrrr-f3jw-mjmc","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-19T14:43:20.441189Z","id":"CVE-2026-45734","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-19T14:43:38.996Z"}}]}}}