CVE-2020-27637
📋 TL;DR
CVE-2020-27637 is a critical path traversal vulnerability in CRAN, R's default package manager, that allows attackers to write arbitrary files outside intended directories during package installation. This affects all R users installing packages via R CMD install or install.packages() function. Successful exploitation can lead to complete server compromise.
💻 Affected Systems
- R programming language with CRAN package manager
📦 What is this software?
Cran by R Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to full system compromise, data theft, and lateral movement within the network.
Likely Case
Arbitrary file write leading to privilege escalation, persistence mechanisms, or denial of service.
If Mitigated
Limited impact if proper file permissions and sandboxing prevent traversal outside user directories.
🎯 Exploit Status
Exploitation requires tricking users into installing malicious packages, which can be achieved through social engineering or compromised repositories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.0.3
Vendor Advisory: https://www.r-project.org/foundation/
Restart Required: No
Instructions:
1. Download R version 4.0.3 or later from https://cran.r-project.org 2. Install the new version following OS-specific instructions 3. Verify installation with R --version
🔧 Temporary Workarounds
Use alternative package manager
allTemporarily use alternative package managers like Bioconductor or manually install packages from verified sources
# Install from Bioconductor
if (!requireNamespace('BiocManager', quietly = TRUE))
install.packages('BiocManager')
BiocManager::install('package_name')
Restrict package installation sources
allConfigure R to only install packages from trusted repositories
# In R console or .Rprofile
options(repos = c(CRAN = 'https://cran.r-project.org'))
# Or set specific trusted mirror
options(repos = c(CRAN = 'https://cloud.r-project.org'))
🧯 If You Can't Patch
- Implement strict network controls to only allow package downloads from trusted CRAN mirrors
- Run R in containerized or sandboxed environments with restricted file system access
🔍 How to Verify
Check if Vulnerable:
Check R version with 'R --version' or within R console with 'R.version$version.string'. If version is earlier than 4.0.3, system is vulnerable.Check Version:
R --versionVerify Fix Applied:
After updating, run 'R --version' to confirm version is 4.0.3 or later. Test package installation from CRAN to ensure functionality.📡 Detection & Monitoring
Log Indicators:
- Unusual package installation attempts from non-standard repositories
- Multiple failed package installations with path traversal patterns
- File write operations outside expected package directories
Network Indicators:
- Downloads from non-CRAN repositories during package installation
- Unusual outbound connections following package installation
SIEM Query:
source="R_logs" AND (event="package_install" AND (repo!="*cran*" OR path="*../*"))