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The vulnerability behind the May 2020 “undisclosed” vBulletin alert is CVE-2020-12720, an incorrect-access-control flaw rated 9.8 Critical under CVSS 3.1 by the National Vulnerability Database (NVD). Administrators should check their forum’s exact vBulletin branch and patch level, then update any affected installation to its corresponding fixed level: 5.5.6pl1, 5.6.0pl1, or 5.6.1pl1.
What the 2020 vBulletin alert means
The alert refers to CVE-2020-12720. The Hacker News reported on May 11, 2020, that vBulletin maintainers had announced an important security patch without initially disclosing the underlying vulnerability. The issue is no longer undisclosed: NVD describes it as incorrect access control in vBulletin. It is a historical vulnerability, not a new 2026 disclosure.
NVD assigns CVE-2020-12720 a CVSS 3.1 base score of 9.8, Critical. Its record also shows a CVSS 2.0 score of 7.5, High; these are scores under different versions of the rating system. See the NVD record for CVE-2020-12720.
Which vBulletin versions are affected?
NVD lists builds before the following patch levels as affected. Check the branch your forum runs; the relevant fixed level depends on that branch.
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| vBulletin branch | Affected versions | Fixed level to confirm |
|---|---|---|
| 5.5.x | Before 5.5.6pl1 | 5.5.6pl1 or later in the applicable branch |
| 5.6.0 | Before 5.6.0pl1 | 5.6.0pl1 or later in the applicable branch |
| 5.6.1 | Before 5.6.1pl1 | 5.6.1pl1 or later in the applicable branch |
These boundaries are specific to CVE-2020-12720; they are not a statement that every vBulletin release is affected. NVD links to a vendor announcement titled “vBulletin 5.6.1 Security Patch Level 1.” Consult the vBulletin security patch announcement for vendor guidance and confirm the current applicable release instructions before changing a live forum.
How to check and respond
- Identify the installed version and patch level. Use your forum’s administration or deployment records to establish the exact vBulletin branch and whether its release includes the relevant “pl1” patch level. Do not rely on the product name alone.
- Compare it with the affected boundary. If the installation is below the corresponding fixed level in the table, treat it as affected by CVE-2020-12720.
- Apply the appropriate vBulletin update. Follow the vendor’s current instructions for the branch in use. The NVD record identifies the vendor advisory, but the precise installation procedure should come from vBulletin rather than an assumed generic patch process.
- Verify the resulting version. After the update, check the installed branch and patch level again and retain the deployment record. If you cannot establish that the installation reached the corresponding fixed level, seek guidance from the vendor or a qualified administrator.
Do not confuse this CVE with later vBulletin reports
Later vulnerability reports are separate issues, not updates to CVE-2020-12720. A 2025 report discusses CVE-2025-48827 and CVE-2025-48828; a July 2026 report concerns CVE-2026-61511. Their version boundaries and remediation guidance must be checked independently. For this 2020 flaw, use the affected-version boundaries in NVD’s CVE-2020-12720 record.
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