Zero-day vulnerability in Synapse

Improper input validation
CVE-2018-10657

The attack was performed on Sunday, April 29 against #matrix:matrix.org and #matrix-dev:matrix.org that made the rooms temporarily unusable.

Vulnerability details

Advisory: SB2018050901 - Remote denial of service in Matrix Synapse

Vulnerable component: Synapse

CVE-ID: CVE-2018-10657

CVSSv3 score: 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

CWE-ID: CWE-20 - Improper input validation

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.

External links:

https://matrix.org/blog/2018/05/01/security-update-synapse-0-28-1/

About zero-day vulnerabilities

Zero-day vulnerability is an undisclosed vulnerability in software that hackers can exploit to compromise computer programs, gain unauthorized access to sensitive data, penetrate networks, etc. We consider vulnerability a zero-day when there is no solution provided from software vendor and the vulnerability is being actively exploited by malicious actors.

Zero-day candidate is a potential zero-day vulnerability in software which might have been used in targeted attacks, however there is no evidence to support this suggestion.