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PatchSiren cyber security CVE debrief

CVE-2016-9415 Mybb CVE debrief

CVE-2016-9415 is a high-severity integrity issue in MyBB and MyBB Merge System before 1.8.8 on Windows. A remote attacker can overwrite arbitrary CSS files through vectors tied to style import, which can alter site presentation and potentially support follow-on tampering. The public reference trail shows vendor release notes and security mailing list discussion before the CVE record was published.

Vendor
Mybb
Product
Merge System
CVSS
HIGH 7.5
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 running MyBB or MyBB Merge System on Windows, especially if the installation is still on a version earlier than 1.8.8. Security teams should care because the issue is remotely reachable and requires no user interaction.

Technical summary

NVD classifies the issue with CVSS 3.0 vector CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N, indicating network reachability, low attack complexity, no privileges required, no user interaction, and a high integrity impact. The CVE description and CPE data scope the vulnerable products to MyBB and MyBB Merge System versions up to 1.8.7 on Windows. NVD also maps the weakness to CWE-284, consistent with an access-control failure around the style import path.

Defensive priority

High. The vulnerability is remotely exploitable and can directly modify site assets. Even without confidentiality or availability impact, unauthorized file overwrite is operationally significant for web-facing forum software.

Recommended defensive actions

  • Upgrade MyBB and MyBB Merge System to version 1.8.8 or later.
  • Confirm whether any Windows-hosted deployments are still running 1.8.7 or earlier.
  • Review CSS files and related web assets for unexpected or unauthorized changes.
  • Verify filesystem permissions for web application directories so application components cannot write beyond intended paths.
  • Use vendor and project release notes and security advisories as the source of truth for any backport or remediation guidance.

Evidence notes

This debrief is based only on the supplied NVD/CVE metadata and the listed public references. The corpus identifies the affected products, version ceiling, Windows scope, CVSS vector, and CWE mapping. The reference list includes MyBB release notes on 2016-10-17 and oss-security posts on 2016-11-10 and 2016-11-18, which predate the CVE record publication on 2017-01-31. No exploit code or unverified implementation details are included.

Sources and references

Verified primary and authoritative sources

  • CVE-2016-9415 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2016-9415

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2016-9415 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2016-9415

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.