CVE-2026-45734

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Source
https://cve.org/CVERecord?id=CVE-2026-45734
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-45734.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-45734
Aliases
  • GHSA-jrrr-f3jw-mjmc
Published
2026-08-18T15:51:07Z
Modified
2026-09-10T03:30:54Z
Severity
  • 5.3 (Medium) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N CVSS Calculator
Summary
MyBB: Default CAPTCHA missing invalidation
Details

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.

Database specific 
{
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
        "CWE-837"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45734.json",
    "unresolved_ranges": [
        {
            "extracted_events": [
                {
                    "fixed": "1.8.40"
                }
            ],
            "source": "AFFECTED_FIELD"
        }
    ]
}
References

Affected packages

Git / github.com/mybb/mybb

Affected ranges

Type
GIT
Repo
https://github.com/mybb/mybb
Events
Introduced
0 Unknown introduced commit / All previous commits are affected
Fixed
c2ed54f9259b9ce05728a9e657169033fe4adffc
Fixed
e9942c6d19ac1709b3df7357cfb8810774c8d3ac
Database specific
Show details 
{
    "source": "REFERENCES"
}

Affected versions

Other
mybb_1800
mybb_1801
mybb_1804
mybb_1805
mybb_1806
mybb_1807
mybb_1808
mybb_1809
mybb_1810
mybb_1811
mybb_1812
mybb_1813
mybb_1814
mybb_1815
mybb_1815_build
mybb_1816
mybb_1816_build
mybb_1817
mybb_1817_build
mybb_1818
mybb_1818_build
mybb_1819
mybb_1819_build
mybb_1820
mybb_1820-rc
mybb_1820_build
mybb_1821
mybb_1821_build
mybb_1821pl1
mybb_1822
mybb_1822_build
mybb_1823
mybb_1823_build
mybb_1827
mybb_1827_build
mybb_1828
mybb_1828_build
mybb_1829
mybb_1831
mybb_1831_build
mybb_1832
mybb_1832_build
mybb_1833
mybb_1833_build
mybb_1834
mybb_1834_build
mybb_1835
mybb_1835_build
mybb_1836
mybb_1837
mybb_1837_build
mybb_1838
mybb_1838_build
mybb_1839
mybb_1839_build
mybb_1840_build

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-45734.json"