What’s Vulnerable › Vulnerabilities

CVE-2020-26890

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 3.0% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-11-24 · updated 2026-06-17
• Weakness: CWE-20

Description

Matrix Synapse before 1.20.0 erroneously permits non-standard NaN, Infinity, and -Infinity JSON values in fields of m.room.member events, allowing remote attackers to execute a denial of service attack against the federation and common Matrix clients. If such a malformed event is accepted into the room's state, the impact is long-lasting and is not fixed by an upgrade to a newer version, requiring the event to be manually redacted instead. Since events are replicated to servers of other room members, the impact is not constrained to the server of the event sender.

Affected products

• Fedoraproject Fedora: 32, 33
• matrix-org synapse: before 1.20.0 — fixed in 1.20.0

How to fix

Upgrade to a fixed version: matrix-org synapse 1.20.0. Check the vendor advisory for mitigations.

References

• https://github.com/matrix-org/synapse/security/advisories/GHSA-4mp3-385r-v63f
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/G7YXMMYQP46PYL664JQUXCA3LPBJU7DQ/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/U34DPP4ZLOEDUY2ZCWOHQPU5GA5LYNUQ/
• https://github.com/matrix-org/synapse/security/advisories/GHSA-4mp3-385r-v63f
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/G7YXMMYQP46PYL664JQUXCA3LPBJU7DQ/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/U34DPP4ZLOEDUY2ZCWOHQPU5GA5LYNUQ/

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