CVE-2021-31357
📋 TL;DR
This CVE describes a command injection vulnerability in tcpdump command processing on Juniper Networks Junos OS Evolved. It allows authenticated users to bypass CLI command restrictions and execute arbitrary shell commands at their assigned privilege level. The vulnerability affects multiple versions of Junos OS Evolved prior to specific patched releases.
💻 Affected Systems
- Juniper Networks Junos OS Evolved
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
An authenticated attacker with restricted CLI access could execute arbitrary shell commands, potentially gaining full administrative control of the device, exfiltrating sensitive data, or disrupting network operations.
Likely Case
An authenticated user with some CLI access could bypass their command restrictions to perform unauthorized actions, modify configurations, or access restricted system information.
If Mitigated
With proper access controls and network segmentation, the impact is limited to the specific device and user's assigned privilege level, preventing lateral movement or broader network compromise.
🎯 Exploit Status
Exploitation requires authenticated CLI access; command injection in tcpdump processing allows bypass of command restrictions
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 20.3R2-S1-EVO, 20.4R2-S2-EVO, 21.1R2-EVO, 21.2R1-S1-EVO, or 21.2R2-EVO
Vendor Advisory: https://kb.juniper.net/JSA11221
Restart Required: Yes
Instructions:
1. Check current version with 'show version'. 2. Download appropriate patched version from Juniper support. 3. Install update following Juniper upgrade procedures. 4. Reboot device to complete installation.
🔧 Temporary Workarounds
Restrict tcpdump command access
allRemove or restrict tcpdump command execution for non-privileged users through Junos configuration
set system login class <class-name> deny-commands "tcpdump"
Implement strict CLI command authorization
allReview and tighten CLI command restrictions for all user classes
show configuration system login
edit system login class <class-name>
🧯 If You Can't Patch
- Implement strict network segmentation to isolate vulnerable devices
- Enforce least privilege access controls and monitor CLI command usage
🔍 How to Verify
Check if Vulnerable:
Run 'show version' and check if version falls within affected ranges: prior to 20.3R2-S1-EVO, 20.4R2-S2-EVO, 21.1R2-EVO, 21.2R1-S1-EVO, or 21.2R2-EVOCheck Version:
show versionVerify Fix Applied:
After patching, verify version is at or above patched releases: 20.3R2-S1-EVO, 20.4R2-S2-EVO, 21.1R2-EVO, 21.2R1-S1-EVO, or 21.2R2-EVO📡 Detection & Monitoring
Log Indicators:
- Unusual tcpdump command usage patterns
- CLI command execution outside user's normal profile
- Shell command execution from CLI users
Network Indicators:
- Unexpected configuration changes
- Unusual outbound connections from network devices
SIEM Query:
source="junos" AND (command="tcpdump" OR command="shell") AND user!="root"