At three o'clock in the middle of the night, my cell phone was vibrating like crazy. In a daze, I grabbed it and saw that the monitoring alert group had brushed three screens of "source HTTP 500 anomaly" and "bandwidth running full 95%". Heart thumped, grabbed the laptop connected to the VPN - the business background has been stuck to open, the source site server load soared to triple digits, real-time traffic charts show that the offshore broiler is thousands of requests per second the scale of the crazy impact of our services. What's the most ironic part? We have obviously smashed the money on a well-known high-defense CDN, this time the protection console is quiet like nothing happened.
This is a typical "high defense CDN is penetrated" scene. Attackers bypassed the CDN protection rules, directly touched your source station IP, this time the so-called trillion cleaning, intelligent WAF all become a pose. I have seen too many teams first reaction is to contact the CDN customer service, restart the server, or even temporarily shut down the business - these operations are either too slow, or equal to suicide.
Today's chat is not a theoretical solution, but a practical emergency manual summarized after I personally stepped on the pit. The next time you find that the CDN is shapeless, follow the steps below, and you can pull your business back to the safe zone in half an hour.
Step 1: Immediately block traffic from directly connected source stations
The first time you realize that you have been penetrated, don't check the logs or look for the cause, save your life first. The fastest way is to block access to all non-CDN return IPs on the firewall or server security group. Take Cloudflare as an example, the official return source IP segment is public, and other vendors such as CDN5 and CDN07 also provide exclusive return source IP lists in the background. Use iptables to block temporarily:
If you use a cloud platform security group (such as AliCloud/AWS), it is faster to modify the rules directly. Note: Be sure to confirm the CDN vendor's return source IP range in advance, otherwise it may mistakenly kill normal traffic.
Step 2: Quickly switch high defense nodes + refresh resolution
Many vendors' high-defense CDNs offer multi-line backup nodes. For example, CDN07's "Emergency Protection Mode" or 08Host's "Resilient Shield Node", these nodes usually have stricter frequency control and authentication policies. Immediately after the console switches nodes, downgrade the DNS TTL to 60 seconds (if previously set high) and force a resolution refresh. Don't count on cache expiration - attackers can't wait for you to wait half an hour.
This is when you can see the importance of selection. I have tested, like CDN5's Anycast network supports second node switching, while some cheap solutions need to manually raise work orders - waiting for work orders in the middle of the night? Waiting for the server room smoke.
Step 3: Trace back to who exactly missed the source station IP
After plugging the loophole, it's time to settle scores. Eighty percent of the source IP exposure is due to configuration oversights. Common leaks include:
Recommend a trick: use different domain names to do multiple DNS resolutions for the same service, and observe which domains resolve to the source IP. for example:
If a domain name resolves directly to the source IP, it means that the resolution configuration does not go to the CDN at all.I have seen a team on DNSPOD with a CNAME, but forgot to delete the previous A record, which is equivalent to opening a backdoor for the attacker.
Step 4: Hardening the Source Site Stealth Strategy
High-defense CDN is not a universal amulet, the source station itself must be "stealth". Recommended a few underhanded tricks:
Sharing a Nginx configuration that I use myself to automatically intercept non-CDN backhaul requests:
Step 5: Verify the effectiveness of the protection and continuously monitor it
After the emergency operation is completed, use the tool to simulate the attack to verify that the protection is effective. We recommend two self-developed widgets:
Also monitor the business delay and error rate. High-defense CDNs may kill normal users (e.g., CAPTCHA popping up too often) after turning on strict protection, so you need to adjust the sensitivity according to your business. Don't be superstitious about "full-automatic intelligent protection" - I've tested it, and at least three of the intelligent modes on the market can't even protect against simple CC attacks.
Sharp tweets about vendor selection
These days, the water in the high-defense CDN market is too deep. Some vendors brag about "2Tbps protection", the actual take the old hardware pile nodes; there are also "shared cleaning pool", a big attack implicates all customers. I measured a small vendor, attack traffic just to 200Gbps the whole region collapsed, customer service actually said "recommended to upgrade to the enterprise version".
Side-by-side comparison of several common service providers:
Sincere advice: do not just look at the offer and parameters, actually build a test environment to play a wave of traffic to try. Once a vendor gave me a demonstration of "successful protection against 500Gbps attacks", and later found that it was an internal brush data - these days even the CDN have to "prevent teammates".
A couple of final zingers.
High-defense CDN penetration is not a technical problem, is the operation and maintenance system and emergency response capabilities of the demon mirror. I've seen teams spend millions of dollars to buy protection, but because of a DNS configuration error, the whole disk collapsed. I've also seen cases where the minimum CDN + self-developed rules are as stable as Mount Tai.
The truly reliable solution is always: assume that the CDN must be penetrated and the source site must be hidden where the enemy cannot find it. The zero-trust principle is always true in cybersecurity.
The next time you encounter a midnight alarm, I hope you'll smile, open your terminal and knock out a set of combos, then go back to sleep.
