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

> Attackers can remove JSON entries from valid signed activities in Mastodon, enabling spoofing and data modification.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Jun 2026
- **Updated:** 25 Jun 2026
- **Also known as:** BIT-mastodon-2026-48028, GHSA-53m7-2wrh-q839

## What is CVE-2026-48028?

CVE-2026-48028 is a medium-severity vulnerability in mastodon, published on 24 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-354 (Improper Validation of Integrity Check Value)

## Which versions are affected by CVE-2026-48028?

1 open source package ship an affected version, including mastodon.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mastodon` | Bitnami | All versions | 4.3.23, 4.4.17, 4.5.10 |

## How do I fix CVE-2026-48028?

Upgrade mastodon to a fixed version for your release line: 4.3.23, 4.4.17 or 4.5.10.

## Is CVE-2026-48028 being exploited?

There is no known exploitation of CVE-2026-48028 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-48028 and fix it if it is affected.

What it is: CVE-2026-48028 is a medium-severity vulnerability in mastodon, published on 24 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-48028 in the wild and no public exploit code.

Affected packages and fixed versions:
- mastodon (Bitnami): affected all versions; fixed in 4.3.23, 4.4.17, 4.5.10

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-48028/ (Markdown: https://insights.sbomify.com/CVE-2026-48028/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-48028
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-48028
- OSV: https://osv.dev/vulnerability/CVE-2026-48028

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-48028/
Summaries are generated and may contain mistakes; the official description above is the record.