CVE-2021-21274
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CVSS Score
V3.1EPSS Score
v2025.03.14There is a 0.6% chance that this vulnerability will be exploited in the wild within the next 30 days.
Attack Vector Metrics
Impact Metrics
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.
Available Exploits
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Affected Products
Affected Versions:
GitHub Security Advisories
Community-driven vulnerability intelligence from GitHub
Advisory Details
Affected Packages
CVSS Scoring
CVSS Score
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
References
Advisory provided by GitHub Security Advisory Database. Published: March 1, 2021, Modified: September 30, 2024