CVE-2016-9403

newreply.php in MyBB (aka MyBulletinBoard) before 1.8.7 and MyBB Merge System before 1.8.7 allows remote attackers to have unspecified impact by leveraging a missing permission check.

Published: 2017-01-31 Last update: 2026-05-13 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2016-9403 is rated High Risk (66/100): CVSS Critical severity, with medium exploitation likelihood (EPSS 5.33%). High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2016-9403

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-03-30 9.71% 5.33% -4.38%
2 2025-03-29 5.33% 9.71% +4.38%
3 2025-03-17 — 5.33% —

Full EPSS history (6 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2016-9403

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.0 CRITICAL
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2016-9403

Affected software / configurations for CVE-2016-9403

Vendor Product Version Raw CPE
mybb merge_system <= 1.8.6 cpe:2.3:a:mybb:merge_system:*:*:*:*:*:*:*:*
mybb mybb <= 1.8.6 cpe:2.3:a:mybb:mybb:*:*:*:*:*:*:*:*

References for CVE-2016-9403

URL Tags
http://www.openwall.com/lists/oss-security/2016/11/10/8 Mailing List Patch Third Party Advisory
http://www.openwall.com/lists/oss-security/2016/11/18/1 Mailing List Patch Third Party Advisory
http://www.securityfocus.com/bid/94395 Third Party Advisory VDB Entry
https://blog.mybb.com/2016/03/11/mybb-1-8-7-merge-system-1-8-7-release/ Patch Release Notes Vendor Advisory
cvelogic Threat Intelligence