CVE-2026-33868
Mastodon has a GET-Based Open Redirect via '/web/%2F<domain>'
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.
CVSS Vector Breakdown
AV:NAttack VectorAC:LAttack ComplexityPR:NPrivileges RequiredUI:RUser InteractionS:UScopeC:NConfidentialityI:LIntegrityA:NAvailabilityWeaknesses
Affected Products
Attack Graph
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Exploitability
MITRE ATT&CK
1 techniqueReferences
Timeline
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