External risk intelligence

Videolabs libmicrodns Compressed Label Double Free Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2020-6072

The vulnerability affects libmicrodns, a library used for mDNS (Multicast DNS) resolution. mDNS is a link-local protocol designed to operate only within a local network segment for service discovery. It is not routable over the public internet, and libraries implementing this protocol are typically restricted to internal local network communication rather than being exposed to external internet traffic.

Videolabs Libmicrodns

0.1.09.0

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This vulnerability involves a flaw in how a specific software library handles network messages, potentially allowing an attacker to execute unauthorized code on affected systems. The main concern is confirming if this library is used within our environment and if it's exposed to such network messages.

Flaw in network message handling.
Crucial to know if we use this library.
Verify relevance and assess exposure.

Attack Path

How an attacker could exploit the issue

An attacker could send a specially crafted mDNS message to a system using the vulnerable library. This message, designed to exploit how compressed labels are parsed, could trigger a double free error. If successful, this could allow an attacker to execute arbitrary code on the target system.

Network access is required.
Parsing compressed mDNS labels triggers the flaw.
Arbitrary code execution is possible.

Live Threat

Current exploitation, exposure, and threat context

A double free vulnerability in libmicrodns's label-parsing functionality could allow an attacker to execute arbitrary code. This could occur when the system parses compressed labels in mDNS messages, and the return value of the `rr_decode` function is not checked, leading to the vulnerability.

Mismatched mDNS message parsing.
Unchecked return value in `rr_decode`.
Potential arbitrary code execution.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in libmicrodns affects applications that handle mDNS messages. Owners of services that rely on mDNS, or the teams managing the underlying operating system if it's a distribution package, should take action. The first practical step is to identify where libmicrodns is deployed, determine its network reachability, and confirm business criticality to prioritize remediation efforts.

Identify affected deployments and owners.
Verify network exposure and business criticality.
Plan remediation based on confirmed risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is libmicrodns and how is it used?

libmicrodns is a lightweight C library developed by Videolabs that enables applications to perform Multicast DNS (mDNS) resolution. It allows devices on a network to discover services—like printers or media players—without needing a traditional DNS server. Software developers integrate this library into their applications so that users can find and connect to networked devices automatically within their local environment.

What does CVE-2020-6072 mean for system security?

This vulnerability is classified as a double free error (CWE-415). It occurs when the software incorrectly manages memory while processing mDNS labels. Because the library fails to verify the success of a specific decoding function, it attempts to release the same memory twice. In the context of CVE-2020-6072, an attacker can leverage this memory management failure to potentially run unauthorized code on the system.

How does an attacker trigger this mDNS flaw?

The flaw is triggered when the library processes a specifically structured mDNS message containing compressed labels. The attacker must be able to send such a message to the target system's network segment. Simply having the library installed is not enough to be compromised; the library must actively parse an incoming, malicious mDNS packet that intentionally targets this parsing logic to cause the memory error.

Is my system at risk from CVE-2020-6072?

Halo Surface Signal indicates that risk is very unlikely for most systems. Because libmicrodns handles mDNS, which is designed for local network segment communication, it is not routable over the public internet. If your systems are not exposed to untrusted traffic on the local network, the surface for this vulnerability is significantly minimized compared to services that are directly reachable from the internet.

What is the first step to address this library vulnerability?

Your priority is to perform an inventory of your software to see if libmicrodns version 0.1.0 or affected Debian packages are in use. Once identified, evaluate the network placement of these applications. If the application handles mDNS traffic from unknown or untrusted sources on your internal network, coordinate with your technical teams to update or patch the library according to the guidance provided by your software or operating system vendor.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.