Severe vBulletin Forum Flaw Enables Remote Code Execution

Critical security flaw in vBulletin’s forum software (tracked as CVE-2024-45721) enables unauthenticated attackers to execute arbitrary code on unpatched systems, potentially compromising millions of online communities.

The vulnerability, discovered by cybersecurity firm SentinelWatch on May 22, 2025, affects vBulletin versions 6.0.0 through 6.1.4 and stems from improper sanitization of user inputs in template rendering modules.

Exploitation attempts surged within 48 hours of public disclosure, with honeypot data showing over 12,000 attack vectors targeting forums in education, gaming, and e-commerce sectors.

vBulletin released patch 6.1.5 on May 25, but 68% of installations remain unupdated as of this reporting.

The vulnerability resides in vBulletin’s vb:raw template directive, which fails to validate nested function calls when processing user-generated content.

Attackers craft malicious forum posts containing payloads like {vb:raw exploit_module.chain(code_execution)}, bypassing built-in sandboxing through parameter smuggling techniques.

Successful exploitation grants SYSTEM-level privileges on Windows hosts and www-data access on Linux systems, enabling installation of web shells, credential harvesters, and cryptocurrency miners.

Proof-of-concept exploits leverage PHP’s unserialize() function with crafted OPcache configurations to bypass disable_functions restrictions.

This allows attackers to execute OS commands via system() calls even when PHP security hardening measures are present.

Network telemetry reveals that 41% of attacks combine this vulnerability with legacy plugin vulnerabilities to establish persistent access.

Current Threat Landscape and Victimology

Between May 22–25, 2025, security teams observed three distinct attack clusters:

1. Cryptojacking Campaigns: 58% of compromised forums had hidden Monero miners installed via obfuscated PowerShell scripts.
2. Data Exfiltration: Attackers cloned user databases from 23 gaming communities containing 14 million records, now circulating on dark web markets.
3. Ransomware Precursors: Six enterprise forums received tailored malware that mapped internal networks for potential Black Basta ransomware deployment.

Notable victims include a European parliamentary discussion board (12,000 users breached) and a healthcare provider’s patient support forum leaking 8,500 medical records.

Cloud-based forum hosts face elevated risks due to shared filesystem permissions amplifying lateral movement capabilities.

Mitigation Strategies and Patch Deployment

vBulletin’s 6.1.5 update introduces granular template validation through a new vb:sanitize directive that enforces strict type checking and function whitelisting. Administrators must:

1. Immediately apply the official patch.
2. Audit template modifications made after January 2025.
3. Rotate all database and SMTP credentials.

For systems requiring delayed patching, security researchers recommend implementing Web Application Firewall (WAF) rules blocking requests containing vb:raw with nested parentheses and restricting PHP’s unserialize() function via php.ini hardening.

The vBulletin Security Response Team has activated a 24/7 support hotline and published a forensic detection toolkit analyzing server logs for IOC patterns like abnormal POST /ajax/render/widget_tabbedcontainer requests.

As forum administrators race to contain breaches, this incident underscores the critical need for zero-day response plans in legacy CMS platforms still widely used across industries.

With exploit kits now automating attacks, complete ecosystem remediation may require months of coordinated security efforts.

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