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Vulnerability record · CVE-2026-22245 · published 8 January 2026

CVE-2026-22245: Joinmastodon mastodon server-side request forgery (ssrf) vulnerability

Joinmastodon · Mastodon

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.

7.1 CVSS 4.0 High EPSS 0.28% · top 81.6% CWE-918 · Server-side request forgery (SSRF)
7.1CVSS 4.0 base score
0.28%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
4References
17 Jun 2026Last modified by NVD

Description

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.

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/mastodon/mastodon/commit/0f4e8a6240b5af1f2c3f34d2793d8610c6ef2aca Patch
https://github.com/mastodon/mastodon/commit/17022907866710a72a1b1fc0a5ce9538bad1b4c3 Patch
https://github.com/mastodon/mastodon/commit/71ae4cf2cf5138ccdda64b1b1d665849b688686d Patch
https://github.com/mastodon/mastodon/security/advisories/GHSA-xfrj-c749-jxxq Vendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.9CVE-2023-36460Joinmastodon mastodon path traversal vulnerabilityMastodon is a free, open-source social network server based on ActivityPub. Starting in version 3.5.0 and prior to versions 3.5.9, 4.0.5, and 4.1.3, …EPSS 40%9.8CVE-2024-23832Joinmastodon mastodon authentication bypass by spoofing vulnerabilityMastodon is a free, open-source social network server based on ActivityPub Mastodon allows configuration of LDAP for authentication. Due to insuffici…EPSS 2.5%9.8CVE-2022-2166Joinmastodon mastodon improper restriction of authentication attempts vulnerabilityImproper Restriction of Excessive Authentication Attempts in GitHub repository mastodon/mastodon prior to 4.0.0.EPSS 1.1%9.8CVE-2022-24307Joinmastodon mastodon incorrect authorization vulnerabilityMastodon before 3.3.2 and 3.4.x before 3.4.6 has incorrect access control because it does not compact incoming signed JSON-LD activities. (JSON-LD si…EPSS 1.4%9.8CVE-2018-21018Joinmastodon mastodon insufficient session expiration vulnerabilityMastodon before 2.6.3 mishandles timeouts of incompletely established sessions.EPSS 2.6%8.2CVE-2026-41259Joinmastodon mastodon vulnerabilityMastodon is a free, open-source social network server based on ActivityPub. Prior to v4.5.9, v4.4.16, and v4.3.22, Mastodon allows restricting new us…EPSS 0.37%8.2CVE-2024-37903Joinmastodon mastodon missing authorization vulnerabilityMastodon is a self-hosted, federated microblogging platform. Starting in version 2.6.0 and prior to versions 4.1.18 and 4.2.10, by crafting specific …EPSS 0.53%7.7CVE-2024-25623Joinmastodon mastodon unrestricted file upload vulnerabilityMastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.2.7, 4.1.15, 4.0.15, and 3.5.19, when fetching remote…EPSS 0.52%

Source: NIST National Vulnerability Database (record CVE-2026-22245), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.