Security readout for executives and security teams
Plain-English summary
MyBB versions 1.8.13 through 1.8.39 can allow an unauthenticated attacker to take control of the forum server when the installer remains available. Crafted database settings can become executable PHP code, enabling data theft, modification, or service disruption. MyBB 1.8.40 fixes the issue.
Executive priority
Treat reachable installers on affected internet-facing systems as an immediate remediation priority. Upgrade promptly and restrict installer access now. For systems where the installer is unavailable, schedule an accelerated upgrade and verify that exposure has not been reintroduced.
Technical view
The installer writes user-supplied database configuration into a PHP configuration file. Its addcslashes() character list omits the backslash, allowing crafted values to escape the generated string and inject PHP code. The network-accessible attack requires no privileges or user interaction but depends on install/index.php being available.
Likely exposure
Exposure is highest for internet-accessible MyBB 1.8.13–1.8.39 deployments where the installer can still be reached. Systems already running 1.8.40 are fixed according to the supplied sources. Deployments without an available installer are less exposed to this specific attack path, although vulnerable installations should still be upgraded.
Exploitation context
The CVSS 3.1 score is 9.8 because exploitation is remotely reachable, low complexity, unauthenticated, and can compromise confidentiality, integrity, and availability. The supplied record does not identify active exploitation, and the CVE is not marked as included in KEV. Do not treat exploitation as confirmed.
Researcher notes
The vulnerable behavior was introduced in MyBB 1.8.13 and fixed in 1.8.40. The distinguishing defect is the missing backslash in the addcslashes() character list used for installer database values. Evidence supports code injection leading to RCE, but the supplied sources provide no confirmation of exploitation in the wild.
Mitigation direction
- Upgrade affected MyBB installations to version 1.8.40 or later.
- Immediately prevent network access to the installer until upgrading.
- Prioritize internet-facing forums whose install/index.php remains reachable.
- Follow the MyBB advisory and release guidance during remediation.
Validation and detection
- Inventory MyBB versions and identify installations below 1.8.40.
- Verify whether install/index.php is reachable from untrusted networks.
- Confirm upgraded systems report MyBB 1.8.40 or later.
- Review configuration files and relevant logs for unexpected changes or installer requests.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-94: Code execution behavior lookup
Code execution and unsafe deserialization weaknesses often justify reviewing execution behavior and process telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupDatabase behavior lookup
The CVE wording references database injection or access, so collection and exfiltration review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-45117 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9GitHub_MVulnerability scoring details
Base CVSS 3.1 score
9.8CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/mybb/mybb/security/advisories/GHSA-gpc4-77rp-3xqrCVE reference, GitHub_M · x_refsource_CONFIRM
- https://github.com/mybb/mybb/commit/0fe713e3b964bfc878ea65bdd9f746f585f6ebbfCVE reference, GitHub_M · x_refsource_MISC
- https://github.com/mybb/mybb/releases/tag/mybb_1840CVE reference, GitHub_M · x_refsource_MISC
- https://mybb.com/versions/1.8.40CVE reference, GitHub_M · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Control of Generation of Code
Improper Control of Generation of Code represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.