03:14 AM – The silence was the first sign.
The Zabbix alerts didn’t trigger because the monitoring VM was the first to have its vmdk headers shredded. I only noticed because the hum of the drive arrays in Rack 4 changed pitch—a frantic, high-frequency seeking sound that tells you the heads are working overtime to destroy your career. By the time I pulled up a console, the Debian 11 Bullseye splash screen was gone, replaced by a grub rescue prompt that couldn’t find the filesystem.
If you’re reading this, kid, it means I finally walked out, or the caffeine finally stopped my heart. You’re sitting in my chair now. Don’t touch the keyboard until you’ve read this log. The “best practices” they taught you in your $5,000 boot camp are useless here. This wasn’t a script kiddie with a Kali ISO; this was a surgical strike on our infrastructure that exploited every single “we’ll fix that later” note I ever wrote.
Table of Contents
The Initial Triage: Why the Backups Failed
The first thing you’ll want to do in a crisis is reach for the backups. Don’t bother. They knew our retention policy better than the CFO does. They didn’t just encrypt the production data; they sat on the network for three weeks, mapping the Veeam service accounts and the secondary storage nodes.
I found the entry point on a legacy Nginx 1.18.0 instance running on an unpatched Ubuntu 18.04 box that some “innovative” dev team stood up for a “three-day pilot” in 2019. It was still there, forgotten, facing the public internet. They used a known exploit to get a shell, then pivoted.
When I checked the backup logs, the corruption was systematic. They didn’t delete the backups—that would have triggered an alert. They modified the backup scripts to pipe /dev/zero into the archive stream after the first 10MB. To the monitoring software, the jobs “completed successfully.” The file sizes looked right. But the data was a void.
Hard-won lesson: If your backups are reachable via the same network they are protecting, they aren’t backups; they’re just extra targets. One of the most vital cybersecurity tips I can give you is this: air-gap your secondary storage. If there isn’t a physical break or a strictly enforced one-way immutable policy (like S3 Object Lock with a compliance timer), you are betting your life on the mercy of a thief.
I tried to run a simple check on the remaining nodes:
# Check for modified binaries in /bin and /usr/bin
find /bin /usr/bin -mtime -3 -ls
# Look for the ransom note across the remaining mounts
grep -r "RESTORE_FILES.txt" /mnt/storage/
The results were a graveyard. Every critical database on the Linux Kernel 5.10.0-23-amd64 clusters was gone. The XFS metadata was scrambled beyond repair.
Tracing the Lateral Movement: The RDP and SSH Pivot
Once they had the Nginx box, they didn’t go for the crown jewels immediately. They were quiet. They used netstat -tulpn to map our internal topology. They saw the management VLAN. They saw that I, in my infinite exhaustion three months ago, had left a password-based SSH login active on a jump box because my YubiKey was acting up.
I found the trace in /var/log/auth.log before the logrotate daemon was killed.
May 14 01:12:34 jump-box-01 sshd[12445]: Accepted password for root from 10.0.4.15 port 44322 ssh2
May 14 01:12:35 jump-box-01 sshd[12445]: pam_unix(sshd:session): session opened for user root by (uid=0)
They didn’t even need an exploit. They just guessed a password that was probably in a wordlist from a 2016 LinkedIn leak. From there, they used the jump box to scan the rest of the subnet.
I ran this to see who else was currently “visiting” our dying kingdom:
# Check active connections and the PIDs associated with them
netstat -atp | grep ESTABLISHED
# Look for suspicious processes running out of /tmp or /dev/shm
ps aux | grep -E 'tmp|shm'
I found a process masquerading as kworker, but it was running out of /dev/shm. It was a reverse shell calling back to an IP in a jurisdiction that doesn’t answer subpoenas.
The attacker had upgraded the OpenSSH 8.4p1 daemon on the jump box to a patched version that logged every keystroke of every admin who logged in after them. They had my credentials. They had the keys to the kingdom because I was too tired to follow my own rules.
Auditing the Kernel and the Shell: Forensic Scavenging
By hour 24, I was vibrating from the sheer volume of espresso and rage. I had to determine if the kernel itself was compromised. On Debian 11, you expect a certain level of integrity, but if they have root, they own the ring 0 space.
I started digging into journalctl to see when the modules were loaded.
# Check for kernel taints and suspicious module loads
journalctl -k | grep -i "taint"
lsmod | cut -d' ' -f1 | xargs modinfo | grep -E "filename|vermagic"
The attackers had loaded a rootkit that hooked the getdents64 system call. This is why ls and find weren’t showing the encryption binaries. They were invisible to the standard user-space tools. I had to boot from a trusted live USB and mount the NVMe drives read-only to see the actual state of the filesystem.
This is where you learn that “security-by-obscurity” is a lie told by people who want to sell you expensive appliances. The attackers knew the Linux VFS (Virtual File System) layer better than I did. They were using iptables to hide their own traffic.
I found their custom rules hidden in a chain I didn’t recognize:
# List all chains, including the ones they tried to hide
iptables -L -n -v --line-numbers
# They had a rule dropping all traffic to the backup subnet except from their IP
iptables -A FORWARD -d 10.0.5.0/24 -j DROP
They had effectively firewalled me out of my own backup network while they worked. It’s a classic move. If you see a drop in traffic to your storage nodes, don’t assume the jobs are finished. Assume someone has cut the line.
Hardening the Kernel: sysctl and the Illusion of Safety
By hour 40, I started the rebuild. I wiped the nodes. I didn’t “clean” them; I nuked them from orbit. Reinstalling Debian 11 from a known-good ISO. But a default install is a death sentence.
If you want to survive the next shift, you need to harden the network stack at the kernel level. The defaults in /etc/sysctl.conf are designed for connectivity, not security. They favor the “seamless” experience that marketing people love, which is just another word for “vulnerable.”
Here is the sysctl.conf I hammered into the new nodes. If you change these, I will haunt you:
# IP Spoofing protection
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1
# Ignore ICMP broadcast requests (prevents Smurf attacks)
net.ipv4.icmp_echo_ignore_broadcasts = 1
# Disable source packet routing
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
# Ignore send redirects
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0
# Block SYN flood attacks
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_max_syn_backlog = 2048
net.ipv4.tcp_synack_retries = 2
net.ipv4.tcp_syn_retries = 5
# Log Martians (packets with impossible source addresses)
net.ipv4.conf.all.log_martians = 1
After applying these with sysctl -p, the network stack becomes significantly less “chatty” and far more resistant to the kind of reconnaissance the attackers used to map our internal routes.
Another one of my cybersecurity tips: the kernel is your last line of defense. If you let it accept redirects or source-routed packets, you’re basically letting the attacker rewrite your routing table from the outside. Don’t be that admin.
Rebuilding the Perimeter: iptables and SSH Hardening
Hour 55. My eyes felt like they were full of broken glass. I had to rebuild the firewall rules. I threw out the “user-friendly” frontends like UFW or Firewalld. They add too much abstraction. I went back to raw iptables.
I locked down the new Nginx 1.18.0 instances. No more “allow all” on port 80 and 443. I implemented rate limiting at the packet level to stop the brute-force attempts before they even hit the application layer.
# Rate limit SSH to prevent brute force
iptables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --set
iptables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --update --seconds 60 --hitcount 4 -j DROP
# Allow established connections
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
# Default Deny Policy
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT ACCEPT
Then I went for the sshd_config. The default OpenSSH 8.4p1 config on Debian is too permissive. I stripped it down. No passwords. No root login. No legacy ciphers.
Edit /etc/ssh/sshd_config and ensure these lines are set:
PermitRootLogin no
MaxAuthTries 3
PubkeyAuthentication yes
PasswordAuthentication no
PermitEmptyPasswords no
ChallengeResponseAuthentication no
UsePAM no
KexAlgorithms [email protected],diffie-hellman-group-exchange-sha256
Ciphers [email protected],[email protected]
MACs [email protected],[email protected]
By forcing Ed25519 keys and disabling PAM, you remove an entire class of credential-stuffing attacks. If a dev complains they can’t log in with their password, tell them to generate a key pair or find a new job. I don’t have the patience for “convenience” anymore. Convenience is what got us 72 hours of downtime and a $2 million ransom demand that we’re currently trying to ignore.
The Human Element: Why Users are the Ultimate Zero-Day
It’s now hour 68. The systems are coming back online. The databases are being restored from the one physical tape drive I insisted on keeping in 2021—the one the CTO called “an archaic waste of space.” Well, that archaic waste of space is currently saving the company.
But here’s the truth: I can harden the kernel, I can write the most elegant iptables rules, and I can lock down SSH until it’s a digital fortress. None of it matters if a user in Accounting clicks on a “PDF” that is actually an executable.
The final of my cybersecurity tips for you, kid: assume the user is already compromised. Segment the network so that Accounting can’t even see the Server VLAN. Use VLAN tagging and strict firewalling between departments.
I found the original “patient zero” while I was tailing the mail logs.
# Searching for the suspicious mail delivery
grep "delivered" /var/log/mail.log | grep -i "invoice"
An “invoice” was sent to a junior clerk. It contained a macro that pulled a payload from a compromised WordPress site. That payload then scanned the local network for the Nginx vulnerability I mentioned earlier. It was a multi-stage execution that exploited human curiosity first and technical debt second.
Modern security isn’t about building a bigger wall; it’s about building a house where every room is locked and requires a different key. If the attacker gets into the kitchen, they shouldn’t be able to get into the bedroom.
I’ve spent the last four hours writing a script to automate the auditing of /var/log/auth.log and /var/log/syslog across the cluster. It’s a hacky Python script, but it works. It looks for patterns of lateral movement—failed logins followed by a successful one from a new IP, or sudo commands that don’t match the user’s typical profile.
# A snippet of the logic I'm leaving you
import re
def detect_lateral_movement(log_file):
with open(log_file, 'r') as f:
for line in f:
if "Accepted password" in line:
# Logic to cross-reference IP with known management IPs
pass
if "sudo: session opened" in line:
# Logic to alert on unusual sudo timing
pass
It’s not “AI-driven threat detection.” It’s just basic logic. Don’t let the vendors sell you on “vibrant” dashboards and “multifaceted” analytics. If you can’t read the raw logs, you don’t know what’s happening on your boxes.
The sun is coming up. I can hear the first of the office staff arriving. They’ll complain that the internet is “slow” because I’ve routed everything through a deep packet inspection proxy now. They’ll complain that they have to use 2FA for every single internal service. Let them complain. Their convenience is the fuel for my nightmares.
I’m leaving my badge on the desk. The documentation for the new VLAN structure is in the red folder. Don’t lose it. If you see a spike in CPU usage on the SQL nodes that doesn’t correlate with user activity, don’t wait for an alert. Kill the process first and ask questions later. In this room, “shoot first” is the only policy that keeps the lights on.
07:42 AM – The rebuild is holding. The coffee is cold. The next shift is your problem. Good luck, you’re going to need it.
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