# CVE-2026-47389: Mastodon SSRF protection bypass in PrivateAddressCheck

Source: https://junglewise.ai/threats/cve-2026-47389-mastodon-ssrf-protection-bypass-in-privateaddresscheck  
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-2026-47389 · Severity: high · CVSS 8.6 · Published 2026-06-24

Mastodon, a popular open-source social networking platform, is vulnerable to a security flaw that allows attackers to trick the server into making unauthorized requests to internal systems. By exploiting how the server handles certain network addresses, an attacker could gain access to sensitive internal data, such as cloud infrastructure credentials or private administrative interfaces. This could lead to the exposure of private configuration details or unauthorized access to the server's hosting environment.

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

## Quick answers

**Is CVE-2026-47389 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-47389 being exploited in the wild.

**How severe is CVE-2026-47389?** High severity, with a CVSS score of 8.6, published 24 June 2026.

**Which products and versions are affected?** Mastodon < 4.5.10, < 4.4.17, < 4.3.23.

**Is there a fix for CVE-2026-47389?** 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-2026-47389 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-47389?** 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 Server-Side Request Forgery (SSRF) vulnerability exists in Mastodon due to an incomplete remediation of a previous flaw (GHSA-xfrj-c749-jxxq). When running on Ruby versions older than 3.4, the 'PrivateAddressCheck.private_address?' method fails to correctly identify IPv4-mapped IPv6 addresses (::ffff:a.b.c.d) as private. An attacker can exploit this by controlling DNS for a domain and publishing an AAAA record pointing to a mapped private address (e.g., loopback, RFC1918, or cloud metadata endpoints like 169.254.169.254). When Mastodon performs an outbound HTTP fetch against such a hostname, it establishes a TCP connection to the internal IPv4 target. This can result in the exposure of sensitive information, including IAM credentials from cloud metadata services. The issue is patched in versions 4.5.10, 4.4.17, and 4.3.23.

## Affected products

- Mastodon Mastodon < 4.5.10, < 4.4.17, < 4.3.23

## Timeline

- 2026-05-20: advisory: GitHub security advisory published
- 2026-06-24: disclosed: CVE published to NVD

## References

- [https://github.com/mastodon/mastodon/security/advisories/GHSA-xx55-4rrg-8xg6](https://github.com/mastodon/mastodon/security/advisories/GHSA-xx55-4rrg-8xg6)

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