CVE-2020-26890 : What You Need to Know

Matrix Synapse before 1.20.0 allows non-standard JSON values in m.room.member events, leading to a denial of service attack. Learn about the impact, affected systems, and mitigation steps.

Understanding CVE-2020-26890

Matrix Synapse vulnerability allowing remote attackers to execute a denial of service attack.

What is CVE-2020-26890?

Matrix Synapse before 1.20.0 permits non-standard JSON values in m.room.member events, enabling a denial of service attack against the federation and Matrix clients.

The Impact of CVE-2020-26890

Attackers can execute a denial of service attack remotely
Malformed events can have a long-lasting impact
Upgrading to a newer version does not fix the issue
Requires manual redaction of the malformed event
Impact extends beyond the event sender's server

Technical Details of CVE-2020-26890

Matrix Synapse vulnerability details.

Vulnerability Description

Erroneous acceptance of non-standard JSON values in m.room.member events
Allows remote attackers to execute denial of service attacks

Affected Systems and Versions

Matrix Synapse versions before 1.20.0

Exploitation Mechanism

Attackers can inject non-standard JSON values into m.room.member events
Impacting federation and common Matrix clients

Mitigation and Prevention

Steps to mitigate the CVE-2020-26890 vulnerability.

Immediate Steps to Take

Apply the necessary patches or updates provided by the vendor
Monitor for any unusual activity on the network
Consider restricting access to affected systems

Long-Term Security Practices

Regularly update and patch software to prevent vulnerabilities
Conduct security audits and assessments periodically

Patching and Updates

Upgrade Matrix Synapse to version 1.20.0 or newer
Manually redact any malformed events in the room's state to mitigate the impact