Mastodon Missing Consent Verification in Feature Collections

Mastodon is a free, open-source social network server based on ActivityPub. In versions there is a missing condition in the check if remote accounts consented to be featured in a remote Collection could lead to attackers bypassing the check and faking consent. An attacker could forge the FeatureAuthorization object that is used to verify consent to be featured in a Collection and thus make it appear as if an account is allowed to be in a Collection when it actually is not. While the FeatureAuthorization must reside on the same domain as the object it is for, a check is missing to make sure said object is actually the same as in the Collection item. This allows an attacker to forge the authorization. Mastodon servers are affected only if running the main branch or nightly builds who have opted into testing the experimental "Collections" feature by setting the environment variable EXPERIMENTAL_FEATURES to a value including collections. This has been patched in version 4.6.0-beta.1.

Casky was already ahead

This CVE exploits attack patterns that Casky's 484matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

Mastodon's missing authorization check in remote Collection features allows attackers to forge FeatureAuthorization objects and bypass consent validation. This vulnerability affects Mastodon server administrators and users whose accounts could be fraudulently featured in remote Collections without permission. The CVSS 7.5 rating reflects the ability to manipulate account visibility and reputation through unauthorized collection membership, potentially enabling social engineering, impersonation, and trust exploitation across federated networks.

Casky's 484 mapped skills detect the attack patterns underlying this vulnerability across MITRE ATT&CK initial access (TA0001), resource development (TA0043), execution (TA0002), persistence (TA0004), and defense evasion (TA0006) techniques. Practitioners using Casky would identify: forged ActivityPub object creation patterns (TA0001), consent bypass logic flaws via extended reasoning analysis of authorization checks, persistence mechanisms through fraudulent collection membership claims (TA0004), and defense evasion through impersonated legitimate federation objects (TA0006). The platform's Claude-powered analysis would surface missing input validation, inadequate cryptographic verification of remote claims, and insufficient state validation—enabling defenders to locate similar missing-condition vulnerabilities in their own ActivityPub implementations before exploitation.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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484 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-47777.

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malware analysis · medium

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MITRE ATT&CK Techniques

TA0001 TA0043 TA0002 TA0004 TA0006

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