CVE-2026-104817 in Misskey
Summary
by MITRE • 10/13/2026
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.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified within the Misskey federated social media platform represents a critical failure in input validation and resource management mechanisms inherent to its unauthenticated fetch-rss API endpoint. Operating between versions 12.112.1 and 2026.7.0, this component allows external actors to initiate RSS feed retrieval operations without requiring authentication credentials. The core technical flaw lies in the absence of rate limiting controls and response-size restrictions, coupled with a synchronous XML parsing implementation. This architectural decision creates a scenario where an attacker can exploit the server's processing capabilities by submitting maliciously crafted or excessively large RSS feeds that trigger unbounded outbound HTTP requests from the Misskey instance itself.
From a technical perspective, the lack of rate limiting permits an attacker to flood the API with rapid-fire requests, leading to resource exhaustion on the host system through CPU and memory saturation. Simultaneously, the synchronous nature of the XML parsing means that each request blocks the processing thread until completion. When combined with unbounded outbound HTTP requests, this allows for significant amplification attacks where the Misskey instance is used as a proxy or amplifier against third-party servers. The server effectively becomes an instrument for distributed denial-of-service operations, consuming its own bandwidth and computational resources while potentially causing collateral damage to external targets through request volume.
The operational impact extends beyond simple resource exhaustion. Because the vulnerability persists even when federation features are disabled, it exposes internal network services that might otherwise be considered isolated from public-facing internet traffic. An attacker can leverage this capability for server-side request forgery and network reconnaissance by probing internal or private IP addresses reachable from the Misskey instance's environment. This transforms a seemingly benign RSS fetching function into a powerful tool for lateral movement within a network, allowing adversaries to map out internal infrastructure, identify open ports, and potentially pivot to more critical systems that are not directly exposed to the public internet.
This vulnerability aligns with Common Weakness Enumeration (CWE) standards, specifically CWE-787: Out-of-bounds Write in contexts involving memory corruption during parsing, though more accurately it maps to CWE-400: Uncontrolled Resource Consumption due to the exhaustion of system resources via unbounded requests and processing. Furthermore, the exploitation technique corresponds to MITRE ATT&CK tactics related to Impact, particularly Denial of Service (T1499), as well as Discovery techniques such as Network Service Scanning (T1046) when used for internal probing. The ability to make outbound HTTP requests also touches upon CWE-918: Server-Side Request Forgery (SSRF), highlighting the risk of unintended data exfiltration or internal network access.
Mitigation strategies must prioritize immediate patching to version 2026.7.0, which addresses these deficiencies by implementing proper rate limiting and response size constraints. In environments where upgrading is not immediately feasible, administrators should configure web application firewalls or reverse proxies in front of the Misskey instance to enforce strict request throttling based on source IP address. Additionally, network segmentation policies should be reviewed to ensure that even if an attacker exploits this vulnerability, their ability to probe internal services is restricted by firewall rules and access control lists. Input validation mechanisms must also be strengthened to reject malformed or excessively large RSS payloads before they reach the synchronous XML parser, thereby reducing the attack surface for resource exhaustion attacks.