Denial of service attack via .well-known lookups

TRUNG BÌNH 6.5CVE-2021-21274 · GHSA-2hwx-mjrm-v3g8 · PYSEC-2021-132 · Công bố 26/02/2021 · cập nhật 17/06/2026

Tóm tắt nhanh

CVE-2021-21274 là lỗ hổng mức TRUNG BÌNH (CVSS 6.5) ảnh hưởng matrix-synapse, synapse (matrix).
Xác suất bị khai thác trong 30 ngày tới (EPSS): 2.2%, cao hơn 82.2% các lỗ hổng khác.
Cách xử lý: cập nhật lên 1.25.0 hoặc mới hơn.

Gói / sản phẩm	Phiên bản bị ảnh hưởng	Phiên bản đã vá
matrix-synapse PyPI	`≥ 0.99.0, < 1.25.0`	`1.25.0`
synapse matrix	`≥ 0.99.0, < 1.25.0`	`1.25.0`

Mô tả

Impact

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.

Patches

Issue is resolved by #8950. A bug not affecting the security aspects of this was fixed in #9108.

Workarounds

The federation_domain_whitelist setting can be used to restrict the homeservers communicated with over federation.

Mô tả của NVD

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.