Mastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.5.8, 4.4.15, and 4.3.21, an unauthenticated Open Redirect vulnerability (CWE-601) exists in the `/web/*` route due to improper handling of URL-encoded path segments. An attacker can craft a specially encoded URL that causes the application to redirect users to an arbitrary external domain, enabling phishing attacks and potential OAuth credential theft. The issue occurs because URL-encoded slashes (`%2F`) bypass Rails path normalization and are interpreted as host-relative redirects. Versions 4.5.8, 4.4.15, and 4.3.21 patch the issue.
History

Mon, 30 Mar 2026 19:15:00 +0000

Type Values Removed Values Added
CPEs cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:*

Mon, 30 Mar 2026 08:15:00 +0000

Type Values Removed Values Added
First Time appeared Joinmastodon
Joinmastodon mastodon
Vendors & Products Joinmastodon
Joinmastodon mastodon

Fri, 27 Mar 2026 20:00:00 +0000

Type Values Removed Values Added
Description Mastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.5.8, 4.4.15, and 4.3.21, an unauthenticated Open Redirect vulnerability (CWE-601) exists in the `/web/*` route due to improper handling of URL-encoded path segments. An attacker can craft a specially encoded URL that causes the application to redirect users to an arbitrary external domain, enabling phishing attacks and potential OAuth credential theft. The issue occurs because URL-encoded slashes (`%2F`) bypass Rails path normalization and are interpreted as host-relative redirects. Versions 4.5.8, 4.4.15, and 4.3.21 patch the issue.
Title Mastodon has a GET-Based Open Redirect via '/web/%2F<domain>'
Weaknesses CWE-601
References
Metrics cvssV3_1

{'score': 4.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published: 2026-03-27T19:50:07.687Z

Updated: 2026-03-31T18:54:24.919Z

Reserved: 2026-03-24T15:10:05.678Z

Link: CVE-2026-33868

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Analyzed

Published: 2026-03-27T20:16:34.333

Modified: 2026-03-30T19:14:17.297

Link: CVE-2026-33868

cve-icon Redhat

No data.