CVE-2026-42462

Deferred Deferred - Pending Action

JSON-LD Signature Bypass in Fedify

Publication date: 2026-06-10

Last updated on: 2026-06-10

Assigner: GitHub, Inc.

Description

Fedify is a TypeScript library for building federated server apps powered by ActivityPub. Prior to versions 1.9.11, 1.10.10, 2.0.18, 2.1.14, and 2.2.3, an attacker can make use of JSON-LD features to restructure a JSON-LD document that would change how Fedify interprets it without changing its Linked Data Signature, allowing them to alter a third-party signed activity they have received. Versions 1.9.11, 1.10.10, 2.0.18, 2.1.14, and 2.2.3 fix the issue.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-06-10

Last Modified

2026-06-10

Generated

2026-07-01

AI Q&A

2026-06-11

EPSS Evaluated

2026-06-30

NVD

CVE-2026-42462

Affected Vendors & Products

Vendor	Product	Version / Range
fedify	fedify	to 2.2.3 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-436	Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.
CWE-180	The product validates input before it is canonicalized, which prevents the product from detecting data that becomes invalid after the canonicalization step.
CWE-347	The product does not verify, or incorrectly verifies, the cryptographic signature for data.
CWE-1289	The product receives an input value that is used as a resource identifier or other type of reference, but it does not validate or incorrectly validates that the input is equivalent to a potentially-unsafe value.

Attack-Flow Graph

Impact Analysis

The vulnerability can allow an attacker to modify signed activities from third parties without invalidating their signatures. This could lead to unauthorized changes in data or actions within applications using the affected Fedify versions, potentially causing integrity issues, misinformation, or unauthorized operations.

Mitigation Strategies

To mitigate this vulnerability, you should upgrade Fedify to one of the fixed versions: 1.9.11, 1.10.10, 2.0.18, 2.1.14, or 2.2.3.

Executive Summary

This vulnerability affects the Fedify TypeScript library used for building federated server applications powered by ActivityPub. Before certain fixed versions, an attacker could exploit JSON-LD features to restructure a JSON-LD document in a way that changes how Fedify interprets it without altering its Linked Data Signature. This manipulation allows the attacker to alter a third-party signed activity they have received.

Compliance Impact

The vulnerability allows attackers to manipulate signed JSON-LD documents without invalidating their signatures, leading to unauthorized modifications of activities processed by ActivityPub implementations.

Such unauthorized modifications could impact data integrity and availability, which are important aspects of compliance with standards like GDPR and HIPAA that require protection of data integrity and prevention of unauthorized data alteration.

However, the provided information does not explicitly describe direct effects on compliance with these regulations.

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