// For flags

CVE-2021-21274

Denial of service attack via .well-known lookups

Severity Score

6.5
*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 1.25.0, a malicious homeserver could redirect requests to their .well-known file to a large file. This can lead to a denial of service attack where homeservers will consume significantly more resources when requesting the .well-known file of a malicious homeserver. This affects any server which accepts federation requests from untrusted servers. Issue is resolved in version 1.25.0. As a workaround the `federation_domain_whitelist` setting can be used to restrict the homeservers communicated with over federation.

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 1.25.0, un servidor doméstico malicioso podía redireccionar las peticiones para su archivo .well-known a un archivo grande. Esto puede conllevar a un ataque de denegación de servicio en el que los servidores domésticos consumirán significativamente más recursos al solicitar el archivo .well-known de un servidor doméstico malicioso. Esto afecta a cualquier servidor que acepte peticiones de federación desde servidores que no sean confiables. El problema es resuelto en versión 1.25.0. Como solución alternativa, el ajuste de "federation_domain_whitelist" puede ser usado para restringir los servidores domésticos que se comunican con la federación

*Credits: N/A
CVSS Scores
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low
Attack Vector
Network
Attack Complexity
Medium
Authentication
None
Confidentiality
None
Integrity
None
Availability
Partial
* Common Vulnerability Scoring System
SSVC
  • Decision:-
Exploitation
-
Automatable
-
Tech. Impact
-
* Organization's Worst-case Scenario
Timeline
  • 2020-12-22 CVE Reserved
  • 2021-02-26 CVE Published
  • 2023-11-12 EPSS Updated
  • 2024-08-03 CVE Updated
  • ---------- Exploited in Wild
  • ---------- KEV Due Date
  • ---------- First Exploit
CWE
  • CWE-400: Uncontrolled Resource Consumption
  • CWE-770: Allocation of Resources Without Limits or Throttling
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"
 >= 0.99.0 < 1.25.0
Search vendor "Matrix" for product "Synapse" and version " >= 0.99.0 < 1.25.0"
-
Affected
Fedoraproject
Search vendor "Fedoraproject"
 Fedora
Search vendor "Fedoraproject" for product "Fedora"
 34
Search vendor "Fedoraproject" for product "Fedora" and version "34"
-
Affected