CVE-2026-27477

MEDIUM EPSS 18.6%
Published Feb 24, 20264mo ago · Modified Jun 17, 20261w ago
4.6 CVSS 4.0
Medium
Find Similar
Published Feb 24, 2026 4mo ago
Last Modified Jun 17, 2026 1w ago

Description

Mastodon is a free, open-source social network server based on ActivityPub. FASP registration requires manual approval by an administrator. In versions 4.4.0 through 4.4.13 and 4.5.0 through 4.5.6, an unauthenticated attacker can register a FASP with an attacker-chosen `base_url` that includes or resolves to a local / internal address, leading to the Mastodon server making requests to that address. This only affects Mastodon servers that have opted in to testing the experimental FASP feature by setting the environment variable `EXPERIMENTAL_FEATURES` to a value including `fasp`. An attacker can force the Mastodon server to make http(s) requests to internal systems. While they cannot control the full URL that is being requested (only the prefix) and cannot see the result of those requests, vulnerabilities or other undesired behavior could be triggered in those systems. The fix is included in the 4.4.14 and 4.5.7 releases. Admins that are actively testing the experimental "fasp" feature should update their systems. Servers not using the experimental feature flag `fasp` are not affected.

CVSS Details

Base Score
4.6
Exploitability
—
Impact
—
Vector string
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/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:X/V:X/RE:X/U:X
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope X

Threat Intelligence

EPSS Exploit Probability
18.6% percentile
Exploit & Patch Status
No Known Exploit
Patch Available

Weaknesses 1

CWE-918 Server-Side Request Forgery (SSRF) Validation

Affected Products 2

VendorProductVersionRange
joinmastodonmastodon*≥4.4.0  –  <4.4.14
joinmastodonmastodon*≥4.5.0  –  <4.5.7

References 2

  • github.com https://github.com/mastodon/mastodon/commit/7b85d2182361e68d51d9a02f94fb1070b5f503b1
    Patch
  • github.com https://github.com/mastodon/mastodon/security/advisories/GHSA-46w6-g98f-wxqm
    PatchVendor Advisory

Remediation

  • github.com https://github.com/mastodon/mastodon/commit/7b85d2182361e68d51d9a02f94fb1070b5f503b1
    Patch
  • github.com https://github.com/mastodon/mastodon/security/advisories/GHSA-46w6-g98f-wxqm
    PatchVendor Advisory