vBulletin, one of the most widely deployed PHP/MySQL forum platforms globally, has recently been found to contain two critical security flaws—CVE-2025-48827 and CVE-2025-48828—that enable unauthenticated attackers to execute arbitrary code on vulnerable installations. These vulnerabilities, first publicly disclosed on May 23, 2025, have already been observed in active exploits, placing countless online communities at significant risk of compromise. BaseForitfy.eu provides annotated CVE reports that include CVSS & EPSS score, CISA KEV if available as well as a Q & A and A.I assistant using all related CVE resources. So follow the links for more in-depth background on these vBulletin vulnerabilties and discover how to mitigate against any potential exploit.

Overview of vBulletin and Its Security Posture

vBulletin has powered online communities since the early 2000s, offering a modular forum solution renowned for its extensibility, mobile APIs, and AJAX-based interfaces. However, this same complexity has historically broadened its attack surface. In May 2025, security researchers demonstrated that certain internal API controllers and template‐rendering functions—originally intended to be inaccessible—could be invoked due to changes in PHP 8.1’s Reflection API and weaknesses in the template engine’s conditional handling. These flaws affect vBulletin 5.0.0 through 5.7.5 and 6.0.0 through 6.0.3 when deployed on PHP 8.1 or later, leaving unpatched instances open to remote code execution (RCE).

CVE-2025-48827: Unauthenticated Protected Method Invocation

CVE-2025-48827 arises from vBulletin’s improper handling of protected API controllers when running on PHP 8.1 or newer. Specifically, attackers can craft requests against /api.php?method=protectedMethod to bypass internal permission checks and invoke sensitive functionality. Once invoked, these methods can be abused to execute arbitrary PHP functions, effectively granting an attacker shell access as the web server user (for example, www-data on Linux). NVD rates CVE-2025-48827 with a CVSS 3.1 score of 10.0 (Critical), reflecting its high severity and ease of exploitation.

CVE-2025-48828: Template Engine Abuse via Alternative Function Syntax

CVE-2025-48828 is rooted in vBulletin’s template rendering system, which fails to properly sanitize “template conditionals” when parsing custom ad templates. By supplying a crafted payload such as a snippet using alternative PHP function invocation syntax—for instance, var_dump("test")—attackers can circumvent “unsafe function” filters and execute arbitrary PHP code within the application context. This flaw was confirmed to be actively exploited in the wild shortly after disclosure. NVD classifies CVE-2025-48828 with a CVSS 3.1 score of 9.0 (Critical) due to its potential for complete system compromise.

Technical Analysis: How the Exploits Work

Both vulnerabilities leverage changes introduced in PHP 8.1, specifically around how protected methods can be accessed via the Reflection API, and weaknesses in vBulletin’s internal function‐filtering mechanisms. In CVE-2025-48827, an attacker sends a request to /api.php?method=protectedMethod without authentication. Under PHP 8.1, vBulletin’s use of Reflection allows this protected method to be invoked indirectly, enabling the execution of internal routines that can be chained into a full RCE.

In CVE-2025-48828, the attacker exploits vB_Api_Ad::replaceAdTemplate() by injecting malicious code into advertisement templates. The template engine’s conditions are parsed in a way that lets constructed payloads bypass static “unsafe function” filters, so long as they use alternate invocation patterns (e.g., `var_dump`("payload")). When the template engine renders these unsafe templates, it executes the injected PHP functions, again leading to a remote, unauthenticated shell on the server.

Evidence of Active Exploitation

Security researcher Egidio Romano (EgiX) first publicly demonstrated proof‐of‐concept (PoC) exploits on May 23, 2025, detailing how both vulnerabilities could be leveraged to achieve RCE. A few days later, Ryan Dewhurst reported seeing live exploitation attempts in honeypot logs, specifically targeting the ajax/api/ad/replaceAdTemplate endpoint, which is leveraged in CVE-2025-48828. The logs indicated that attackers were deploying PHP backdoors to execute system commands, with some tracing attempts originating from Poland. While Dewhurst’s observations focused primarily on CVE-2025-48828 (template engine abuse), the existence of publicly available Nuclei templates since May 24, 2025, suggests both flaws are easily discoverable and exploitable.

Impacted Versions and Patch Status

The following vBulletin versions are confirmed vulnerable when run on PHP 8.1 or later:

• 5.0.0 through 5.7.5
• 6.0.0 through 6.0.3

Admins are urged to verify whether their installations match these versions. Notably, vBulletin released patches quietly in late 2024—vBulletin 5.7.5 Patch Level 3 and all vBulletin 6.* Patch Level 1 releases—to remediate both flaws. However, many administrators failed to apply these updates, leaving instances exposed. The current, unaffected release is vBulletin 6.1.1; any installation on this version or later is not vulnerable to CVE-2025-48827 or CVE-2025-48828.

Mitigation and Best Practices

• Immediate Upgrade: All vBulletin instances running on PHP 8.1 or above should be updated to version 6.1.1. If upgrading directly is not feasible, apply at least:
  • vBulletin 5.7.5 Patch Level 3 (addresses both CVEs)
  • vBulletin 6.0.3 Patch Level 1 (addresses both CVEs)
  • vBulletin 6.0.2 Patch Level 1 or 6.0.1 Patch Level 1 if on older 6.* branches
• PHP Version Audit: Administrators using PHP 8.1 or newer should audit for any vBulletin installations that might have bypassed update schedules. On PHP versions prior to 8.1, these particular flaws cannot be activated due to missing Reflection API behavior changes. However, running on outdated PHP versions carries its own risks.
• Web Application Firewall (WAF) Rules: Deploy or update WAF signatures to detect anomalous requests against /api.php?method=protectedMethod and /ajax/api/ad/replaceAdTemplate. While not a replacement for patching, WAF rules can provide temporary mitigations against automated exploit tools.
• Regular Patch Management: This incident underscores the necessity of implementing automated patch management. Manual patching can leave critical gaps; organizations should integrate vulnerability scanning and patch orchestration to minimize window of exposure.

Recommendations for vBulletin Administrators

• Inventory and Version Control: Maintain an accurate inventory of all vBulletin forums, including version numbers and PHP runtime environments.
• Enable Two-Factor Authentication (2FA): For administrative accounts, enforce 2FA to reduce risk of credential theft even if an attacker achieves code execution.
• Isolate and Harden: Consider running forum applications within containerized environments or segregated subnets, limiting lateral movement if exploitation occurs.
• Log Monitoring: Enable detailed logging of web requests and monitor for suspicious patterns, such as repeated calls to endpoints like replaceAdTemplate or api.php?method=protectedMethod.
• Incident Response Plan: Have a plan in place to quickly respond to active exploits, including taking vulnerable instances offline, restoring from secure backups, and performing full system audits.

Conclusion

The discovery and swift exploitation of CVE-2025-48827 and CVE-2025-48828 serve as a stark reminder that even well-established applications can harbor catastrophic vulnerabilities when underpinned by shifting dependencies like PHP 8.1. Administrators who assume older patches suffice may find themselves compromised—attackers have demonstrated full RCE capability as recently as late May 2025. To safeguard thriving online communities, immediate action to verify patch status, upgrade to vBulletin 6.1.1, and enforce robust patch management workflows is imperative. Failure to do so will leave forums susceptible to data theft, defacement, or use as pivot points for broader network intrusions.

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