myBB version 1.6.4 was distributed with an unauthorized backdoor embedded in the source code. The backdoor allowed remote attackers to execute arbitrary PHP code by injecting payloads into a specially crafted collapsed cookie. This vulnerability was introduced during packaging and was not part of the intended application logic. Exploitation requires no authentication and results in full compromise of the web server under the context of the web application.
CVE-2011-10018
Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2025-08-13. NVD baseline CVSS 9.8; sources differ by 0.0.
- High severity, but no confirmed exploitation yet
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 9.8
- EG Score
- 9.8(medium)
- EPSS
- 78.4%
- KEV
- Not listed
Published
August 13, 2025
Last Modified
August 14, 2025
Advisory Details (4)
Auto-updated Jun 6, 2026myBB 1.6.4 Backdoor Arbitrary Command Execution | Advisories | VulnCheck
https://www.vulncheck.com/advisories/mybb-backdoor-arbitrary-command-executionMyBB Compromised Source Packages Backdoor Security Issue - Secunia.com
https://web.archive.org/web/20111015224948/http://secunia.com/advisories/46300/1.6.4 Security Vulnerability | MyBB Blog
https://blog.mybb.com/2011/10/06/1-6-4-security-vulnerabilit/Weakness Classification(2)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 9× in last 7d / 39× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-07-22 21:47 UTCEG score recompute
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Publicly available exploits
(1 reference)Working exploit code is in the public domain (1 Metasploit module). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.
- Metasploitexploit/unix/webapp/mybb_backdoor✓ verifiedFirst seen Oct 6, 2011
myBB 1.6.4 Backdoor Arbitrary Command Execution
Open source ↗
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Frequently asked(5)
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Dependency Blast Radius
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