# CVE-2026-48028: Mastodon spoofing via JSON entry removal in signed activities

Source: https://junglewise.ai/threats/cve-2026-48028-mastodon-spoofing-via-json-entry-removal-in-signed-activities  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-24. Updated: 2026-06-24  
License: CC BY 4.0 with a link back

CVE-2026-48028 · Severity: medium · CVSS 6.5 · Published 2026-06-24

Mastodon is an open-source social networking platform. A security flaw in how the software processes incoming messages allows attackers to selectively remove or hide parts of a post while keeping the digital signature valid. This could be used to spoof or manipulate the content of messages received from other users, potentially leading to misinformation or the unauthorized modification of shared data.

Technologies: [Mastodon](https://junglewise.ai/threats/technologies/mastodon). Vendors: [Mastodon](https://junglewise.ai/threats/vendors/mastodon).

## Quick answers

**Is CVE-2026-48028 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-48028 being exploited in the wild.

**How severe is CVE-2026-48028?** Medium severity, with a CVSS score of 6.5, published 24 June 2026.

**Which products and versions are affected?** Mastodon < 4.3.23, >= 4.4.0-beta.1 < 4.4.17, >= 4.5.0-beta.1 < 4.5.10.

**Is there a fix for CVE-2026-48028?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-48028 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-48028?** Check whether you run Mastodon at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A vulnerability exists in Mastodon's normalization process for incoming activities signed with Linked-Data Signatures (LDS). Due to improper validation of the integrity check value (CWE-354), an attacker who obtains a valid signed activity—for example, via ActivityPub inbox forwarding or a shared relay—can selectively remove JSON entries from the object. The Mastodon server will then recognize the modified object as a complete and validly signed activity. This allows for a specific class of spoofing where the integrity of the message is compromised without invalidating the cryptographic signature. The issue is resolved in versions 4.5.10, 4.4.17, and 4.3.23.

## Affected products

- Mastodon Mastodon < 4.3.23, >= 4.4.0-beta.1 < 4.4.17, >= 4.5.0-beta.1 < 4.5.10

## Timeline

- 2026-05-20: advisory: GitHub advisory published by Mastodon maintainers
- 2026-06-24: disclosed: CVE published to NVD

## References

- [https://github.com/mastodon/mastodon/security/advisories/GHSA-53m7-2wrh-q839](https://github.com/mastodon/mastodon/security/advisories/GHSA-53m7-2wrh-q839)

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- [Mastodon signature bypass via JSON-LD restructuring](https://junglewise.ai/threats/cve-2026-46349-mastodon-signature-bypass-via-json-ld-restructuring)