Vulnerability identifier: #VU12518

Vulnerability risk: Medium

CVSSv3.1: 8.2 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:H/RL:O/RC:C]

CVE-ID: CVE-2018-10657

CWE-ID: CWE-20

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Synapse
Server applications / Conferencing, Collaboration and VoIP solutions

Vendor: Matrix.org

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

The vulnerability exists due to an input validation error where malicious events injected with depth = 2^63 - 1 render rooms unusable, related to federation/federation_base.py and handlers/message.py. A remote attacker can send malicious messages and perform a denial of service attack.

Note: this vulnerability has been exploited in the wild in April 2018.

Mitigation
Update to version 0.28.1.

Vulnerable software versions

Synapse: 0.28.0

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External links
http://github.com/matrix-org/synapse/commit/33f469ba19586bbafa0cf2c7d7c35463bdab87eb
http://matrix.org/blog/2018/05/01/security-update-synapse-0-28-1/

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

Yes. This vulnerability is being exploited in the wild.