CVE-2026-33868
Mastodon has a GET-Based Open Redirect via '/web/%2F<domain>'
MEDIUM 6.1EPSS 0.6%
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.
- Affected
- mastodon
- CVSS v3.1 NVD
- 6.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - CVSS v3.1 GITHUB
- 4.3 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N - EPSS
- 0.55% chance of exploitation in the next 30 days, 45th percentile
- Nuclei
- medium · CWE-601
- Published
- 2026-03-27
- Updated
- 2026-03-31