EUVD-2026-61020Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Network unauthenticated RCE, but AC:H reflects the required non-default precondition that the installer remains reachable; full compromise gives C/I/A:H.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
Lifecycle Timeline
4DescriptionCVE.org
MyBB is free and open source forum software. From 1.8.13 until 1.8.40, the installer module does not properly escape user-supplied database configuration values written to the configuration file, resulting in PHP code injection and remote code execution when the installer is available. install/index.php processes the values with addcslashes(), but the $characters argument added in MyBB 1.8.13 does not include the backslash character, allowing crafted input to escape the generated PHP string. The uniquely identifying implementation details include introduced in MyBB 1.8.13. This issue is fixed in version 1.8.40.
AnalysisAI
Remote code execution in MyBB 1.8.13 through 1.8.39 lets an attacker inject arbitrary PHP into the generated database configuration file when the web-based installer (install/index.php) remains accessible. The installer sanitizes database configuration values with addcslashes() but omits the backslash from its escaped-character set, so crafted input can break out of the single-quoted PHP string and execute attacker-controlled code. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the web installer (install/index.php) to be reachable over HTTP - typically during initial setup, or on servers where the install/ directory was not deleted or locked after installation. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N, C:H/I:H/A:H) describes an unauthenticated, network, low-complexity full-compromise RCE, which drives the 9.8 score. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Vendor-released patch: MyBB 1.8.40 - upgrade to this version, which changes the addcslashes() escape set from "'" to "\\'" so the backslash is escaped (fix commit 0fe713e3b964bfc878ea65bdd9f746f585f6ebbf, https://github.com/mybb/mybb/releases/tag/mybb_1840). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: audit all MyBB instances to identify vulnerable versions (1.8.13-1.8.39) and confirm whether install/index.php is externally reachable; immediately block access to the install/ directory using web server rules or firewall controls to prevent exploitation. …
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Same weakness CWE-94 – Code Injection
View allSame technique Code Injection
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External POC / Exploit Code
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