CVE-2021-42021 – This CVE describes a path traversal vulnerabili... (How to Fix)

Q: What is the severity of CVE-2021-42021?

CVE-2021-42021 has a CVSS score of 7.5 (HIGH). This CVE describes a path traversal vulnerability in Siemens Siveillance Video DLNA Server that allows unauthenticated remote attackers to read arbitrary files outside the web directory. Affected systems include multiple versions from 2019 R1 through 2021 R1. Successful exploitation could expose sensitive server files and enable follow-on attacks.

📋 TL;DR

This CVE describes a path traversal vulnerability in Siemens Siveillance Video DLNA Server that allows unauthenticated remote attackers to read arbitrary files outside the web directory. Affected systems include multiple versions from 2019 R1 through 2021 R1. Successful exploitation could expose sensitive server files and enable follow-on attacks.

💻 Affected Systems

Products:

Siveillance Video DLNA Server

Versions: 2019 R1, 2019 R2, 2019 R3, 2020 R1, 2020 R2, 2020 R3, 2021 R1

Operating Systems: Windows

Default Config Vulnerable: ⚠️ Yes

Notes: DLNA servers are often exposed to internal networks for media streaming purposes.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Attackers could read sensitive system files (passwords, configuration files, private keys), potentially leading to full system compromise or lateral movement within the network.

🟠

Likely Case

Unauthenticated attackers reading application configuration files, logs, or other sensitive data stored on the server, enabling reconnaissance for further attacks.

🟢

If Mitigated

With proper network segmentation and access controls, impact would be limited to the isolated DLNA server environment.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Path traversal vulnerabilities typically have low exploitation complexity and require minimal attacker skill.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Update to Siveillance Video 2021 R2 or later

Vendor Advisory: https://cert-portal.siemens.com/productcert/pdf/ssa-755517.pdf

Restart Required: Yes

Instructions:

1. Download latest Siveillance Video version from Siemens support portal. 2. Backup current configuration. 3. Install update following vendor instructions. 4. Restart DLNA service.

🔧 Temporary Workarounds

Network Segmentation

all

Isolate DLNA server from untrusted networks using firewall rules

Access Control

all

Restrict network access to DLNA server to only trusted devices/VLANs

🧯 If You Can't Patch

Implement strict network segmentation to isolate DLNA server from untrusted networks
Deploy web application firewall (WAF) with path traversal protection rules

🔍 How to Verify

Check if Vulnerable:

Check Siveillance Video version in administration interface or Windows Programs and Features

Check Version:

Check via Siveillance Video web interface or Windows Control Panel > Programs and Features

Verify Fix Applied:

Verify version is 2021 R2 or later and test path traversal attempts return proper access denied errors

📡 Detection & Monitoring

Log Indicators:

Unusual file access patterns in DLNA server logs
Multiple failed path traversal attempts

Network Indicators:

HTTP requests containing '../' sequences to DLNA server
Unusual file downloads from DLNA server

SIEM Query:

source="DLNA_Server" AND (uri="*../*" OR status=403 OR status=404)

📊 Metadata

CVE ID: CVE-2021-42021

CVSS v3 Score: 7.5 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CWE: CWE-26

Published: November 9, 2021

Last Updated: November 21, 2024

🔗 References

https://cert-portal.siemens.com/productcert/pdf/ssa-755517.pdf Patch,Third Party Advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-755517.pdf Patch,Third Party Advisory

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