# CVE-2026-72916 — mastodon

> As of 2026-08-10, CVE-2026-72916 is a Medium-severity (band derived from the CVSS v4.0 score, not stated by the CNA) vulnerability in mastodon, CVSS v4.0 6.3, EPSS 0.3% (28.7th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-72916 as of 2026-08-10; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-08-10

## What is CVE-2026-72916?

Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1, PrivateAddressCheck.private_address? in app/lib/private_address_check.rb normalized IPv4-mapped IPv6 addresses but did not recognize IPv4-compatible IPv6 addresses with IPAddr#ipv4_compat?. An attacker could supply an address in the omitted range to bypass the ALLOWED_PRIVATE_ADDRESSES protection and make Mastodon send HTTP requests to loopback interfaces, potentially accessing private resources and services. Exploitation requires a system that supports the obsolete IPv4-compatible IPv6 mechanism. This issue is fixed in versions 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1.

The record classifies CVE-2026-72916 under weakness classes [CWE-918](https://intel.threadlinqs.com/cwe/CWE-918), [CWE-1286](https://cwe.mitre.org/data/definitions/1286.html). 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 56 days ago.

## Severity and exploitation probability

- **CVSS v4.0 base score:** 6.3 — Medium (derived from score) (`CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:L`)
- **EPSS (FIRST):** 0.3% probability of exploitation in the next 30 days, higher than 28.7% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4.3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-08-10

## Is CVE-2026-72916 being exploited?

It currently carries a trending score of 37 in the Threadlinqs vulnerability feed.

## Affected products and versions

- **mastodon**: mastodon

## How to fix CVE-2026-72916

No vendor patch reference has been recorded for CVE-2026-72916 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-72916

No threat campaign in the Threadlinqs corpus currently references CVE-2026-72916, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, FIRST EPSS. Last verified by Threadlinqs on 2026-08-12. This product uses the NVD API but is not endorsed or certified by the NVD.

**Vendor advisory and patch**

- [github.com](https://github.com/mastodon/mastodon/security/advisories/GHSA-vwhj-3g83-v276)

**Other references**

- [github.com](https://github.com/mastodon/mastodon/commit/18c61f286f1f5718a8f517940ba384866ffa3892)
- [github.com (467c933459c7d0e5513475b9e4888afaedfb1074)](https://github.com/mastodon/mastodon/commit/467c933459c7d0e5513475b9e4888afaedfb1074)
- [github.com (930aa9fee26bf9eaefe27826fa1061288d83373b)](https://github.com/mastodon/mastodon/commit/930aa9fee26bf9eaefe27826fa1061288d83373b)
- [github.com (da47a1bd3cd07935d7ca55a1f4f1a76f7f167e0d)](https://github.com/mastodon/mastodon/commit/da47a1bd3cd07935d7ca55a1f4f1a76f7f167e0d)
- [github.com (v4.4)](https://github.com/mastodon/mastodon/releases/tag/v4.4.21)

_Showing 6 of 9 recorded references._

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-72916
Full detection coverage and IOCs for threats exploiting CVE-2026-72916 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp