EUVD-2026-61021Severity by source
AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
Remote, low-complexity, unauthenticated delivery but requires a victim click (UI:R); reflected XSS impact is scope-changing into the browser (S:C) yet realistically bounded to the victim's session, so C:L/I:L rather than H.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
Lifecycle Timeline
4DescriptionCVE.org
MyBB is free and open source forum software. Prior to 1.8.40, the Contact module does not validate a redirect URL or protocol correctly, resulting in an open redirect and reflected JavaScript code injection. contact.php accepts the redirect target from the from HTTP parameter in $mybb->input['from'] or the Referer HTTP header in $_SERVER['HTTP_REFERER'] and passes it to redirect() without sufficient verification. A javascript: URI becomes the target of the Click here if you don't want to wait any longer link because $force_redirect is true, allowing script execution when a victim selects the link. This issue is fixed in version 1.8.40.
AnalysisAI
Reflected JavaScript injection and open redirect in MyBB forum software before 1.8.40 lets a remote attacker execute script in a victim's browser session. The Contact module (contact.php) takes a redirect target from the 'from' request parameter or the Referer header and passes it to redirect() without validating the URL scheme, so a javascript: URI can be delivered as the destination of the post-submission 'Click here if you don't want to wait any longer' link. …
Unlock full vulnerability intelligence
- Risk assessment & exploitation conditions
- Attack chain visualization
- Remediation with exact patch versions
- Threat intelligence from 22 sources
- Personal watchlist & email alerts
Free forever · No credit card required
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the target forum to have the Contact module (contact.php) enabled - MyBB's default configuration - and requires the victim to actively click the 'Click here if you don't want to wait any longer' fallback link that is rendered because $force_redirect is true. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N) drives the 9.3 rating largely through the scope-change and high confidentiality/integrity flags typical of client-side script execution, but the UI:R requirement is the key tempering factor: exploitation is not automatic and depends on a victim clicking a crafted link, so this behaves more like targeted phishing-assisted XSS than a wormable, self-propagating flaw. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker crafts a link to the target forum's contact.php with the 'from' parameter set to a javascript: URI (or sends a request that seeds a malicious Referer) and lures a logged-in user - ideally an administrator - to submit the contact form and then click the 'Click here if you don't want to wait any longer' fallback link. The script runs in the victim's authenticated session, enabling cookie/session theft or actions performed as that user. … |
| Remediation | Vendor-released patch: 1.8.40 - upgrade MyBB to 1.8.40, which corrects contact.php to validate the redirect URL and reject non-http(s) schemes; follow the release notes at https://github.com/mybb/mybb/releases/tag/mybb_1840 and the advisory GHSA-wf92-5q5h-qr53. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Identify all MyBB installations across your infrastructure and document running versions; alert forum administrators, security teams, and stakeholders of the critical vulnerability affecting user sessions. …
Sign in for detailed remediation steps and compensating controls.
Threat intelligence, references, and detailed analysis are available after sign-in.
sapi/cgi/cgi_main.c in PHP before 5.3.12 and 5.4.x before 5.4.2, when configured as a CGI script (aka php-cgi), does not
(1) boardData102.php, (2) boardData103.php, (3) boardDataJP.php, (4) boardDataNA.php, and (5) boardDataWW.php in Netgear
The '/common/download_agent_installer.php' script in the Quest KACE System Management Appliance 8.0.318 is accessible by
ProjectSend versions prior to r1720 are affected by an improper authentication vulnerability. Rated critical severity (C
Roundcube Webmail contains a critical PHP object deserialization vulnerability (CVE-2025-49113, CVSS 9.9) that allows au
Util/PHP/eval-stdin.php in PHPUnit before 4.8.28 and 5.x before 5.6.3 allows remote attackers to execute arbitrary PHP c
Palo Alto Networks PAN-OS management web interface contains an authentication bypass allowing unauthenticated attackers
Nagios XI version xi-5.7.5 is affected by OS command injection. Rated high severity (CVSS 8.8), this vulnerability is re
Nagios XI version xi-5.7.5 is affected by OS command injection. Rated high severity (CVSS 8.8), this vulnerability is re
The get_referers function in /opt/ws/bin/sblistpack in Sophos Web Appliance before 3.7.9.1 and 3.8 before 3.8.1.1 allows
The Backup Migration plugin for WordPress is vulnerable to Remote Code Execution in all versions up to, and including, 1
NetAlertX (formerly PiAlert) versions 23.01.14 through 24.x before 24.10.12 allow unauthenticated command injection thro
Share
External POC / Exploit Code
Leaving vuln.today