Denial of service in Matrix Synapse

1) Input validation error

EUVDB-ID: #VU48685

Risk: Medium

CVSSv3.1: 5 [CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C]

CVE-ID: CVE-2020-26890

CWE-ID: CWE-20 - Improper input validation

Exploit availability: No

Description

The vulnerability allows a remote user to perform a denial of service (DoS) attack.

The vulnerability exists due to the application 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.

Mitigation

Install updates from vendor's website.

Vulnerable software versions

Synapse: 0.0.0 - 2.20.15.1104

External links

http://github.com/matrix-org/synapse/security/advisories/GHSA-4mp3-385r-v63f

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote authenticated user via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.