CVE-2026-104817

Deferred Deferred - Pending Action

Unauthenticated DoS via Unrestricted RSS Fetch in Misskey

Publication date: 2026-10-13

Last updated on: 2026-10-16

Assigner: GitHub, Inc.

Description

Misskey is an open source, federated social media platform. From 12.112.1 until 2026.7.0, the unauthenticated fetch-rss API lacks rate limiting and response-size restrictions and performs synchronous XML parsing. An attacker can trigger unbounded outbound HTTP requests and synchronous parsing, exhausting instance resources, amplifying requests toward third-party servers, or probing network-reachable services even when federation is disabled. This issue is fixed in version 2026.7.0.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-10-13

Last Modified

2026-10-16

Generated

2026-10-19

AI Q&A

2026-10-14

EPSS Evaluated

2026-10-18

NVD

CVE-2026-104817

EUVD

EUVD-2026-99239

Affected Vendors & Products

Vendor	Product	Version / Range
misskey-dev	misskey	>= 12.0.0, <= 13.14.2
misskey-dev	misskey	>= 2023.9.0-beta.1, < 2026.7.0

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-918	The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.
CWE-770	The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
CWE-405	The product does not properly control situations in which an adversary can cause the product to consume or produce excessive resources without requiring the adversary to invest equivalent work or otherwise prove authorization, i.e., the adversary's influence is "asymmetric."

Attack-Flow Graph

Executive Summary

This vulnerability affects Misskey, a federated social media platform, where the unauthenticated fetch-rss API lacks rate limiting and response-size restrictions. It performs synchronous XML parsing, allowing attackers to trigger unbounded outbound HTTP requests and exhaust instance resources. This can cause denial of service, amplify requests to third-party servers, or probe network services even if federation is disabled.

Detection Guidance

Monitor for unusual outbound HTTP traffic patterns, especially from the /api/fetch-rss endpoint. Check for excessive resource usage like CPU or memory spikes during RSS fetch operations. Inspect logs for repeated failed requests or large response sizes from the fetch-rss API.

Impact Analysis

An attacker could exploit this to overload your Misskey server, causing downtime or slow performance. They might also use your server to amplify attacks on other systems or scan internal network services, potentially exposing sensitive information or disrupting operations.

Mitigation Strategies

Block access to the /api/fetch-rss endpoint at the reverse proxy level as a temporary mitigation. Update Misskey to version 2026.7.0 or later to apply the permanent fix which includes rate limiting, response size limits, and concurrency controls.

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