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CVE-2021-27890

43
FAUCET Score

CVE-2021-27890 is a high-severity SQL Injection vulnerability affecting MyBB versions prior to 1.8.26, specifically through theme properties within theme XML files. With a CVSS score of 8.8 (High), this vulnerability allows an unauthenticated attacker to achieve high impact on confidentiality, integrity, and availability with low attack complexity, requiring user interaction. While not listed in CISA's KEV catalog, exploit code for a chained remote command execution is available on ExploitDB, and it has garnered some community discussion, indicating potential for exploitation.

Impacted Technologies

VendorProductVersion(s)CPE
< 1.8.26CPE matchmatch criteria
cpe:2.3:a:mybb:mybb:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

8.8HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
2.8
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
10.59%
Probability of exploitation in next 30 days
EPSS Percentile
95.3%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
ExploitDB: EDB-49696 · Mar 22, 2021
This CVE's current EPSS score of 0.1059 is in the 95th percentile among its peer group of 14,875 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.2 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.1 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

github_advisorypatch availablevia nvd_reference
View patch

References

packetstormsecurity.com / files/161908/MyBB-1.8.25-Remote-Command-Execution.html
Third Party AdvisoryVDB Entry
blog.sonarsource.com / mybb-remote-code-execution-chain
ExploitThird Party Advisory
github.com / mybb/mybb/security/advisories/GHSA-r34m-ccm8-mfhq
PatchRelease NotesThird Party Advisory