// For flags

CVE-2021-29471

Denial of service in Matrix Synapse

Severity Score

5.3
*CVSS v3.1

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

0
*Multiple Sources

Exploited in Wild

-
*KEV

Decision

-
*SSVC
Descriptions

Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.33.2 "Push rules" can specify conditions under which they will match, including `event_match`, which matches event content against a pattern including wildcards. Certain patterns can cause very poor performance in the matching engine, leading to a denial-of-service when processing moderate length events. The issue is patched in version 1.33.2. A potential workaround might be to prevent users from making custom push rules, by blocking such requests at a reverse-proxy.

Synapse es un servidor doméstico de referencia de Matrix escrito en python (paquete pypi matrix-synapse). Matrix es un ecosistema para VoIP y mensajería instantánea federada abierta. En Synapse versiones anteriores a 1.33.2, unas "Push rules" pueden especificar condiciones bajo las cuales coincidirán, incluyendo "event_match", que compara el contenido del evento con un patrón que incluye comodines. Determinados patrones pueden causar un rendimiento muy deficiente en el motor de coincidencia, conllevando a una denegación de servicio cuando se procesan eventos de duración moderada. El problema está parcheado en versión 1.33.2. Una posible solución alternativa podría ser impedir a unos usuarios crear reglas de inserción personalizadas, al bloquear dichas peticiones en un proxy inverso

*Credits: N/A
CVSS Scores
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low
Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low
Attack Vector
Network
Attack Complexity
Low
Authentication
None
Confidentiality
None
Integrity
None
Availability
Partial
* Common Vulnerability Scoring System
SSVC
  • Decision:-
Exploitation
-
Automatable
-
Tech. Impact
-
* Organization's Worst-case Scenario
Timeline
  • 2021-03-30 CVE Reserved
  • 2021-05-11 CVE Published
  • 2024-01-25 EPSS Updated
  • 2024-08-03 CVE Updated
  • ---------- Exploited in Wild
  • ---------- KEV Due Date
  • ---------- First Exploit
CWE
  • CWE-331: Insufficient Entropy
  • CWE-400: Uncontrolled Resource Consumption
CAPEC
Affected Vendors, Products, and Versions
Vendor Product Version Other Status
Vendor Product Version Other Status <-- --> Vendor Product Version Other Status
Matrix
Search vendor "Matrix"
 Synapse
Search vendor "Matrix" for product "Synapse"
 < 1.33.2
Search vendor "Matrix" for product "Synapse" and version " < 1.33.2"
-
Affected
Fedoraproject
Search vendor "Fedoraproject"
 Fedora
Search vendor "Fedoraproject" for product "Fedora"
 34
Search vendor "Fedoraproject" for product "Fedora" and version "34"
-
Affected