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PatchSiren cyber security CVE debrief

CVE-2016-9405 Mybb CVE debrief

CVE-2016-9405 is a cross-site scripting issue in MyBB and MyBB Merge System member validation. The NVD record classifies it as medium severity and identifies affected versions through 1.8.6. Because the flaw can let an attacker inject script or HTML, administrators should treat any exposed validation workflow as sensitive until patched.

Vendor
Mybb
Product
CVE-2016-9405
CVSS
MEDIUM 6.1
CISA KEV
Not listed in stored evidence
Original CVE published
2017-01-31
Original CVE updated
2026-05-13
Advisory published
2017-01-31
Advisory updated
2026-05-13

Who should care

Administrators and developers running MyBB or MyBB Merge System versions before 1.8.7 should pay attention, especially if member validation content is displayed back to users or staff. Security teams should also review any custom themes, plugins, or templates that render validation-related data.

Technical summary

The NVD record maps CVE-2016-9405 to CWE-79 (cross-site scripting) in member validation. Affected CPE criteria cover MyBB and MyBB Merge System through 1.8.6. The CVSS 3.0 vector (AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N) indicates network reachability, no privileges required, user interaction needed, and limited confidentiality and integrity impact with scope change.

Defensive priority

Medium priority. The issue is externally reachable and requires user interaction, so it is not an emergency by itself, but it should be patched promptly on any exposed installation because XSS can affect user sessions and trust boundaries.

Recommended defensive actions

  • Upgrade MyBB and MyBB Merge System to 1.8.7 or later.
  • Review member validation pages and any related templates for proper output encoding.
  • Ensure any user-supplied or validation-related fields are escaped before rendering in HTML.
  • Check custom plugins or themes that may bypass the vendor's fixed handling.
  • Monitor for unexpected script or HTML injection attempts in forum workflows.

Evidence notes

This debrief is based on the supplied NVD CVE record, which identifies CWE-79, affected versions through 1.8.6, and the CVSS 3.0 vector AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N. The record also cites vendor release notes and mailing-list references as supporting material. The exact injection vector is not specified in the source corpus.

Official resources

The CVE was published in the supplied record on 2017-01-31. The NVD references include vendor release notes and mailing-list advisories from 2016, indicating remediation information was available before the CVE publication date.