CVE-2021-42139
📋 TL;DR
CVE-2021-42139 is a critical code injection vulnerability in Deno Standard Modules that allows remote code execution when processing untrusted YAML files. Attackers can execute arbitrary code on affected systems by crafting malicious YAML content. This affects any application using vulnerable Deno Standard Modules versions to parse YAML files from untrusted sources.
💻 Affected Systems
- Deno Standard Modules
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with remote code execution, allowing attackers to install malware, exfiltrate data, or pivot to other systems.
Likely Case
Remote code execution leading to data theft, service disruption, or lateral movement within the network.
If Mitigated
Limited impact if proper input validation and sandboxing are implemented, potentially reduced to denial of service.
🎯 Exploit Status
Exploitation requires the application to parse attacker-controlled YAML content. The vulnerability is well-documented with public proof-of-concept available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.107.0
Vendor Advisory: https://github.com/denoland/deno_std/releases/tag/0.107.0
Restart Required: No
Instructions:
1. Update Deno Standard Modules to version 0.107.0 or later. 2. Update package dependencies: 'deno cache --reload' or equivalent. 3. Rebuild and redeploy affected applications.
🔧 Temporary Workarounds
Disable YAML parsing
allRemove or disable YAML parsing functionality in affected applications
Remove 'import { parse } from "https://deno.land/std@<0.107.0/encoding/yaml.ts";' from code
Use alternative YAML library
allReplace vulnerable YAML parser with a secure alternative like js-yaml
npm install js-yaml
import yaml from 'js-yaml';
🧯 If You Can't Patch
- Implement strict input validation and sanitization for all YAML input
- Run Deno applications with minimal permissions using --allow-* flags to limit damage
🔍 How to Verify
Check if Vulnerable:
Check if your application imports YAML parsing from Deno Standard Modules versions before 0.107.0Check Version:
deno --version | grep stdVerify Fix Applied:
Verify that Deno Standard Modules version is 0.107.0 or later and no vulnerable imports remain📡 Detection & Monitoring
Log Indicators:
- Unexpected process execution from YAML parsing context
- Errors in YAML parsing with suspicious content
- Unusual network connections from Deno processes
Network Indicators:
- Outbound connections from applications that should only parse YAML
- Traffic to unexpected destinations following YAML processing
SIEM Query:
process.name: "deno" AND process.cmdline: *yaml* AND (process.cmdline: *eval* OR process.cmdline: *exec*)