SSRF in Joinmastodon Mastodon
CVE-2026-22245
Mastodon is a free, open-source social network server based on ActivityPub. By nature, Mastodon performs a lot of outbound requests to user-provided domains. Mastodon, however, has some protection mechanism to disallow requests to local IP addresses (unless specified in `ALLOWED_PRIVATE_ADDRESSES`) to avoid the "confused deputy" problem. The list of disallowed IP address ranges was lacking some IP address ranges that can be used to reach local IP addresses. An attacker can use an IP address in the affected ranges to make Mastodon perform HTTP requests against loopback or local network hosts, potentially allowing access to otherwise private resources and services. This is fixed in Mastodon v4.5.4, v4.4.11, v4.3.17 and v4.2.29.
Vulnerability class: SSRF (Server-Side Request Forgery)
EPSS: 0.003 (17.1th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
Affected products
- Joinmastodon Mastodon
- Mastodon — versions < 4.2.29, >= 4.3.0-beta.1, < 4.3.17, >= 4.4.0-beta.1, < 4.4.11
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
- security-advisories@github.com (Patch, x_refsource_MISC)
- security-advisories@github.com (Patch, x_refsource_MISC)
Frequently asked questions
- What is CVE-2026-22245?
- CVE-2026-22245 is a high-severity vulnerability in Joinmastodon Mastodon, classified under Server-Side Request Forgery (SSRF). CVSS score: 7.5/10. Published 2026-01-08.
- How severe is CVE-2026-22245?
- High severity. CVSS v3 base score is 7.5 out of 10.