CVE-2026-33868 PoC — Mastodon has a GET-Based Open Redirect via '/web/%2F<domain>'

Source

https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-33868.yaml

Associated Vulnerability

Title: Mastodon has a GET-Based Open Redirect via '/web/%2F<domain>' (CVE-2026-33868)
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.

Description

Mastodon version < 4.5.8, < 4.4.15, < 4.3.21 is vulnerable to unauthenticated Open Redirect vulnerability (CWE-601) exists in the /web/* route due to improper handling of URL-encoded path segments.

File Snapshot

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