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How the Vulnerability Works
The CVE-2025-30399 vulnerability in .NET 8.0 and 9.0 arises due to improper handling of file paths in the runtime, allowing an attacker to place malicious files in specific directories. When the application loads dependencies or configuration files, it fails to enforce proper path validation, leading to unintended code execution. The exploit leverages directory traversal or symlink attacks to trick the runtime into loading attacker-controlled binaries. This bypasses security checks, enabling remote attackers to execute arbitrary code in the context of the application.
DailyCVE Form
Platform: .NET
Version: 8.0.16, 9.0.5
Vulnerability: RCE
Severity: Critical
Date: June 10, 2025
Prediction: Patch by June 25, 2025
What Undercode Say:
Exploitation Analysis
- Attack Vector: File write in `/tmp` or application directories.
2. Trigger: Malicious DLL/JSON loading via path traversal.
3. Impact: Full system compromise under app privileges.
Detection & Mitigation
- Check installed versions:
dotnet --info | grep "Version"
- Apply patches immediately:
sudo apt update && sudo apt install dotnet-sdk-9.0=9.0.6
- Restrict file permissions:
chmod -R 750 /var/www/.dotnet
Exploit PoC (Hypothetical)
// Malicious payload in crafted JSON
{
"Payload": "../../../malicious.dll"
}
Defensive Code Snippet
// Validate paths before loading
string safePath = Path.GetFullPath(userInput).Replace("..", "");
if (!safePath.StartsWith("/valid/app/path"))
throw new SecurityException("Invalid path");
Network-Level Protection
Block suspicious .NET runtime spawns iptables -A OUTPUT -p tcp --dport 443 -m owner --uid-owner dotnetuser -j DROP
Log Monitoring
Audit .NET file access auditctl -w /usr/share/dotnet -p war -k dotnet_access
Expected Patch Behavior
Microsoft will enforce strict path validation in `Microsoft.NetCore.App.Runtime` v9.0.6/8.0.17, preventing traversal attacks.
Post-Patch Actions
- Recompile self-contained apps.
- Revoke temporary file write permissions.
- Monitor `dotnet_telemetry.log` for anomalies.
References
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
