CVE-2026-104445 in YesWiki
Summary
by MITRE • 10/02/2026
YesWiki before 4.6.7 contains an authentication bypass vulnerability in the ActivityPub inbox that fails to bind the verified HTTP signature signer to the activity actor. Unauthenticated attackers with any ActivityPub keypair can send signed Delete or Update activities referencing a mirrored entry's sourceUrl to delete or overwrite other actors' federated entries.
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Analysis
by VulDB Data Team • 10/02/2026
YesWiki versions prior to 4.6.7 are affected by a critical authentication bypass vulnerability located within the ActivityPub inbox handler, specifically designated as CWE-287 Improper Authentication. This flaw stems from a fundamental logic error in how the platform processes federated social media activities. The system correctly verifies the cryptographic signature of incoming HTTP requests to ensure they originate from a valid keypair associated with an ActivityPub actor. However, it fails to enforce strict binding between this verified signer and the actual actor identified within the activity payload's "actor" field. This decoupling allows for significant identity spoofing capabilities where the entity signing the message is not required to match the entity claiming authorship in the data structure itself.
The operational impact of this vulnerability is severe, enabling unauthenticated attackers with access to any valid ActivityPub keypair to manipulate federated content on behalf of other users. By crafting malicious Delete or Update activities that reference a mirrored entry's sourceUrl, an attacker can trick the YesWiki instance into removing or overwriting entries belonging to different actors. This effectively allows for unauthorized deletion of user-generated content and potential defacement through forced updates. The vulnerability undermines the integrity guarantees provided by the ActivityPub protocol, which relies on cryptographic signatures to establish trust in federated interactions. Attackers do not need valid credentials for the target account; they only require their own keypair to sign a message that falsely attributes actions to another user's identity within the federation network.
This type of vulnerability aligns with MITRE ATT&CK technique T1078 Valid Accounts, as it involves impersonating legitimate users through protocol manipulation rather than credential theft. It also relates to CWE-345 Insufficient Verification of Data Authenticity because the system accepts data based on a signature that does not correspond to the claimed source. The ability to delete or overwrite federated entries disrupts the availability and integrity of information shared across the fediverse, potentially causing data loss for legitimate users whose content is mirrored in the YesWiki instance.
Mitigation strategies must prioritize immediate upgrading to version 4.6.7 or later, where this binding logic has been corrected to ensure that the signer's public key matches the actor field in every incoming activity. For organizations unable to upgrade immediately, implementing a Web Application Firewall rule set capable of inspecting ActivityPub payloads may provide partial protection by validating signature-to-actor consistency before processing. Additionally, administrators should review access logs for unusual patterns of Delete or Update activities originating from unexpected IP addresses or keypairs and consider temporarily disabling the ActivityPub inbox feature if federation is not actively required. Regular auditing of federated content integrity can help detect any successful exploitation attempts that may have occurred prior to remediation.