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CVE-2019-12831

24
FAUCET Score

CVE-2019-12831 is a critical remote code execution vulnerability affecting MyBB versions prior to 1.8.21. Attackers can exploit a MySQL string truncation behavior during a crafted XML theme import to create a PHP shell in the forum's cache directory. This high-severity flaw (CVSS 7.2) allows for complete compromise of confidentiality, integrity, and availability with low attack complexity, requiring high privileges. There is currently no evidence of active exploitation, public exploit code, or significant community discussion surrounding this vulnerability.

Impacted Technologies

VendorProductVersion(s)CPE
< 1.8.21CPE matchmatch criteria
cpe:2.3:a:mybb:mybb:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

7.2HIGH

CVSS:3.0/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
HIGH
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
1.2
Impact Score
5.9
CvssVersion
3.0

Exploit Intelligence

EPSS Score
1.49%
Probability of exploitation in next 30 days
EPSS Percentile
71.5%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0149 is in the 65th percentile among its peer group of 5,538 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.3 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

blog.mybb.com / 2019/06/10/mybb-1-8-21-released-security-maintenance-release
Release NotesVendor Advisory
blog.ripstech.com / 2019/mybb-stored-xss-to-rce
ExploitVendor Advisory