CVE-2021-27116
📋 TL;DR
This vulnerability in Beego's MemProf function allows local attackers to perform symlink attacks, potentially overwriting arbitrary files on the system. It affects all users running Beego web framework versions up to 2.0.2. The attack requires local access to the system where Beego is running.
💻 Affected Systems
- Beego web framework
📦 What is this software?
Beego by Beego
⚠️ Risk & Real-World Impact
Worst Case
Attacker gains root privileges by overwriting critical system files like /etc/passwd or /etc/shadow, leading to complete system compromise.
Likely Case
Local user escalates privileges by overwriting configuration files or gaining unauthorized access to sensitive data.
If Mitigated
Attack limited to file overwrites within the application's directory with proper file permissions and isolation.
🎯 Exploit Status
Exploitation requires local access to the system and knowledge of the target file paths. The symlink attack technique is well-known and easy to implement.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.0.3 and later
Vendor Advisory: https://github.com/beego/beego/issues/4484
Restart Required: Yes
Instructions:
1. Update Beego to version 2.0.3 or later using 'go get -u github.com/beego/beego/v2@v2.0.3' 2. Rebuild and redeploy your application 3. Restart the Beego service
🔧 Temporary Workarounds
Disable memory profiling
allDisable the MemProf functionality if not required
Set EnableMemProf = false in your Beego configuration
Restrict file permissions
linuxRun Beego with minimal privileges and restrict write access to sensitive directories
chmod 755 /path/to/beego/directories
run beego as non-root user
🧯 If You Can't Patch
- Run Beego application in a container with restricted filesystem access
- Implement strict file permission controls and run the application with minimal privileges
🔍 How to Verify
Check if Vulnerable:
Check Beego version in go.mod or via 'beego version' command. If version is 2.0.2 or earlier and MemProf is enabled, system is vulnerable.Check Version:
beego versionVerify Fix Applied:
Verify Beego version is 2.0.3 or later and test that symlink attacks against the MemProf endpoint are blocked.📡 Detection & Monitoring
Log Indicators:
- Multiple failed attempts to access memory profiling endpoints
- Unusual file creation/modification in Beego directories
Network Indicators:
- Local connections to memory profiling ports (typically 8088)
SIEM Query:
source="beego.log" AND ("MemProf" OR "memory profile") AND (response_code="200" OR "file operation")