Block or Challenge High-Risk Cloud ASN using Cloudflare

This rule creates a "Digital Border" that blocks or challenges traffic originating from 8 specific Cloud Hosting Providers (VPS/Data Centers).
The Logic: Real humans browse forums from Residential ISPs (Comcast, Jio, Vodafone). Traffic from these ASNs (DigitalOcean, Hetzner, Tencent) is 99% non-human: Bots, Scrapers, DDoS scripts, or VPNs.

Forum Administrators often try to block bad actors by IP address. This is a losing battle because attackers on cloud platforms can rotate IPs in seconds.
The rule provided targets the ASN (Autonomous System Number)—the unique ID of the hosting company itself. By targeting the ASN, you block the entire infrastructure the attacker is using, regardless of which IP they rotate to.

The Exact Rule

Code Select Expand

(ip.src.asnum in {14061 24940 20473 63949 132203 45102 31898 139341 })

Why You Must Block These Specific ASNs
These 8 providers are the "Super-Carriers" of automated web traffic. Here is exactly who you are blocking and why:

• 14061 (DigitalOcean): The #1 source of "low-effort" forum spam and registration bots due to cheap, disposable droplets.
  
• 24940 (Hetzner Online): A German provider with massive bandwidth. Often used for high-speed scrapers that clone your content to train AI models or steal SEO rankings.
  
• 20473 (Vultr): A major competitor to DigitalOcean; frequently used for hosting private VPNs and brute-force scripts.
  
• 63949 (Linode / Akamai): Historically a source of SSH scanners and vulnerability probes.
  
• 132203 (Tencent Cloud): The primary source of unsolicited traffic from mainland China.
  
• 45102 (Alibaba Cloud): The "AWS of China." Often hosts heavy e-commerce scrapers.
  
• 31898 (Oracle Cloud): Heavily abused recently due to their "Always Free" VPS tier, allowing attackers to run bots at zero cost.
  
• 139341 (Aceville Pte Ltd): The Hidden Threat. This is the Singapore-based CDN arm of Tencent. Many admins block Tencent (132203) but miss Aceville, allowing the bots to simply route through Singapore.
  

Step-by-Step Guide (Implementation)

• Step 1: Access WAF Custom Rules
  Navigate to Security > WAF > Custom Rules in your Cloudflare dashboard.
  
• Step 2: Enter the Expression
  Click "Edit Expression" and paste the exact rule provided above.
  
• Step 3: Select Action
  Recommended Action: Managed Challenge.
  Reason: A small percentage of real users (privacy enthusiasts) route their traffic through these clouds via private VPNs. A "Challenge" lets them solve a CAPTCHA to enter, while "Block" kills them instantly. Bots cannot solve the CAPTCHA.
  

How It Works & Hidden Details
The "Residential vs. Commercial" Split:
The internet is divided into ASN types.

* ISP/Residential: (Your Users). Low risk.
* Hosting/Business: (These ASNs). High risk.
When you apply this rule, you are essentially saying: "If you are coming from a server farm, you must prove you are human."

The AI Scraper Defense (2025 Context):
AI companies (LLMs) rent thousands of servers on Hetzner (24940) and DigitalOcean (14061) to scrape forum conversations for training data. This rule is your primary defense against your community's content being harvested without your permission.

Things to Watch Out For

• Risk 1: VPN False Positives. If your forum has a highly technical user base (sysadmins, coders), many of them might use their own VPNs hosted on Linode or Vultr. Expect a few complaints if you set the action to "Block" instead of "Challenge."
  
• Risk 2: Uptime Monitors. If you use a server monitor like UptimeRobot or Pingdom, check if they use these cloud providers. You might accidentally block your own monitoring alerts.
  

Update: Additional Details & Recent Changes

• The AI Scraper Shift (2025-26):
  The motivation for blocking these ASNs has shifted. While it used to be about "forum spam," in 2026, the primary threat from Hetzner (24940) and DigitalOcean (14061) is AI Data Harvesting. LLM crawlers (like `Bytespider` for TikTok/ByteDance or `ClaudeBot`) aggressively use these cheap cloud providers to scrape your community content to train their models without permission. This rule is now your primary defense against "Model Collapse" caused by excessive scraping.
• Aceville (139341) - The "Singapore Bypass":
  In 2025, attackers began mass-migrating to Aceville (Tencent's global CDN arm) specifically because many old WAF lists blocked Tencent China (132203) but whitelisted Singapore. If you block Tencent but leave Aceville open, you are blocking 0% of the actual attack traffic.
• Oracle "Always Free" Abuse (ASN 31898):
  Oracle Cloud's "Always Free" tier (2 AMD VMs + 4 ARM Ampere instances) has become the #1 platform for running "residential-like" proxy networks. Because these IPs are stable and high-speed, attackers use them to tunnel traffic that looks semi-legitimate. A "Managed Challenge" here is mandatory.
• Managed Challenge vs. Block:
  Cloudflare's "Managed Challenge" is superior to "Block" for these ASNs. Many legitimate tech users (your core audience) use self-hosted VPNs on Linode or Vultr for privacy. If you "Block," you kill them. If you "Challenge," they see a 1-second spinning wheel and pass through, while the bots get stuck.