Log in Start free

Vulnerability · Published Feb 26, 2021 · Assigned by GitHub_M

CVE-2021-21274Denial of service attack via .well-known lookups

Medium 4.3

In plain English

A medium-severity uncontrolled resource consumption in synapse from matrix-org. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 2.2% (higher than 82% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)4.3Medium
Exploit odds (30 days)2.2%top 17.7% of all CVEs
Exploited in the wildNo reportsnot in CISA KEV
Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:14matrix-synapse1.25.0-1DEBIAN-CVE-2021-21274
PyPImatrix-synapse1.25.0GHSA-2hwx-mjrm-v3g8
PyPImatrix-synapse1.25.0PYSEC-2021-132

Affected products (as reported)

VendorProductVersions
matrix-org synapse >=0.99.0, < 1.25.0

Weakness: CWE-400 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L

References