dnsmasq by Simon Kelley (Update A)
Monitor4ICS-CERT ICSA-21-019-01Jan 19, 2021
Attack VectorNetwork
Auth RequiredNone
ComplexityHigh
User InteractionNone needed
Summary
dnsmasq open-source DNS component versions before 2.83 contain three vulnerabilities (CVE-2020-25684 through CVE-2020-25686) that fail to properly validate DNS responses, allowing DNS spoofing attacks. The vulnerabilities affect Siemens RUGGEDCOM RM1224, SCALANCE M-800, SCALANCE S615, SCALANCE SC-600, and SCALANCE W1750D devices that rely on dnsmasq for DNS resolution. An attacker can send crafted DNS responses to redirect queries to malicious servers without needing credentials or user interaction. Siemens has released patches for most products (firmware 6.4 for RM1224/M-800/S615, 2.1.3 for SC-600) but states SCALANCE W1750D has no fix planned.
What this means
What could happen
An attacker could redirect DNS traffic from affected network devices to malicious servers, potentially causing the device to connect to wrong control servers or receive incorrect operational commands. For devices without patches available, DNS spoofing could be a persistent threat requiring compensating controls.
Who's at risk
Siemens industrial network devices that use dnsmasq for DNS services: RUGGEDCOM RM1224 and SCALANCE M-800, S615, and SC-600 series managed switches used in industrial networks for edge routing and security; SCALANCE W1750D wireless access points. Water utilities and electric utilities using these devices for control network communications are affected.
How it could be exploited
An attacker with network access to the same Layer 2 network or upstream from the affected device could send specially crafted DNS responses that bypass dnsmasq validation logic, redirecting DNS queries to malicious servers. The attacker does not need valid credentials or to interact with users.
Prerequisites
- Network access to Layer 2 network or upstream DNS path
- Ability to send crafted DNS responses before legitimate responses arrive
- dnsmasq service active and processing DNS queries
remotely exploitableno authentication requiredlow complexityno patch available for SCALANCE W1750Daffects network-critical infrastructure devices
Exploitability
Low exploit probability (EPSS 0.5%)
Affected products (5)
4 with fix1 EOL
ProductAffected VersionsFix Status
RUGGEDCOM RM1224<V6.46.4
SCALANCE M-800<V6.46.4
SCALANCE S615<V6.46.4
SCALANCE SC-600<V2.1.32.1.3
SCALANCE W1750DAll versionsNo fix (EOL)
Remediation & Mitigation
0/7
Do now
0/4SCALANCE W1750D
HARDENINGFor SCALANCE W1750D and other devices without patches, implement Layer 2 security features such as DHCP snooping and IP source guard
All products
HARDENINGConfigure dnsmasq to not listen on WAN (wide area network) interfaces if DNS queries from external networks are not required
WORKAROUNDReduce the maximum DNS queries dnsmasq forwards by setting --dns-forward-max parameter to a lower value (less than default of 150)
WORKAROUNDDisable DNSSEC validation in dnsmasq temporarily until patches are applied
Schedule — requires maintenance window
0/3Patching may require device reboot — plan for process interruption
RUGGEDCOM RM1224
HOTFIXUpdate RUGGEDCOM RM1224, SCALANCE M-800, SCALANCE S615 to firmware version 6.4 or later
SCALANCE SC-600
HOTFIXUpdate SCALANCE SC-600 to firmware version 2.1.3 or later
All products
HARDENINGConfigure upstream DNS connections to use DNS-over-HTTPS or DNS-over-TLS encryption
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