CVE-2026-45734

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{"affected": [{"affectedData": [{"product": "mybb", "vendor": "mybb", "versions": [{"status": "affected", "version": "< 1.8.40"}]}], "source": "security-advisories@github.com"}], "cveTags": [], "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."}], "id": "CVE-2026-45734", "lastModified": "2026-09-08T21:02:26.047", "metrics": {"cvssMetricV31": [{"cvssData": {"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"}, "exploitabilityScore": 3.9, "impactScore": 1.4, "source": "security-advisories@github.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-45734", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-08-19T14:43:20.441189Z", "version": "2.0.3"}}]}, "published": "2026-08-18T16:17:08.980", "references": [{"source": "security-advisories@github.com", "url": "https://github.com/mybb/mybb/commit/c2ed54f9259b9ce05728a9e657169033fe4adffc"}, {"source": "security-advisories@github.com", "url": "https://github.com/mybb/mybb/releases/tag/mybb_1840"}, {"source": "security-advisories@github.com", "url": "https://github.com/mybb/mybb/security/advisories/GHSA-jrrr-f3jw-mjmc"}, {"source": "security-advisories@github.com", "url": "https://mybb.com/versions/1.8.40"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Deferred", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-837"}], "source": "security-advisories@github.com", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0,1.8.40)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "mybb", "source": "cna", "vendor": "mybb"}, "product": "mybb", "vendor": "mybb"}], "created": "2026-08-18T18:00:04.363546+00:00", "updated": "2026-08-18T18:00:04.559327+00:00", "vendors": ["mybb", "mybb$PRODUCT$mybb"]}