CVE-2026-27477
Mastodon is a free, open-source social network server based on ActivityPub.
Published Feb 24, 2026 · updated Jun 17, 2026 · joinmastodon mastodon
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 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 to a value including . 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 are not affected.
Code
The project this record applies to. Exploit listings stay in References.
Timeline
Detection, updates, and resolution for this record.
Feb 24, 2026 · NIST NVD
Detected
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 that includes or resolves to a local / internal address, leading to the Mastodon server making requests to that address. This only
Jun 17, 2026 · NIST NVD
Updated
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 that includes or resolves to a local / internal address, leading to the Mastodon server making requests to that address. This only
Affected
- cpe joinmastodon/mastodonversion unspecified
Sources
- CVE.orgVulnerability recordCVE-2026-27477
Official CVE identifier
cve.org - NIST NVDVulnerability recordCVE-2026-27477
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
nvd.nist.gov