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CVE-2026-46482

MediumCVSS 5.3 / 10
Published Aug 18, 2026·Last modified Aug 20, 2026
Affected Components(56)
mybb/mybb
mybb_1833_build
mybb/mybb
mybb_1822
mybb/mybb
mybb_1835_build
1 / 19
Description

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

Details

The public Registration workflow (member.php?action=do_register) 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 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.

Risk Scores
Base Score
5.3

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the integrity of the data.

Threat Intelligence
4.9

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
0.33%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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Medium severity2026 vulnerabilities
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