CVE-2026-33868

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 v3 4.3 MEDIUM

4.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact NONE

Integrity Impact LOW

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/mastodon/mastodon/security/advisories/GHSA-xqw8-4j56-5hj6	Vendor Advisory

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:joinmastodon:mastodon::::::::
	cpe:2.3:a:joinmastodon:mastodon::::::::
	cpe:2.3:a:joinmastodon:mastodon::::::::

History

No history.

Information

Published : 2026-03-27 20:16

Updated : 2026-06-17 10:38

NVD link : CVE-2026-33868

Mitre link : CVE-2026-33868

CVE.ORG link : CVE-2026-33868

JSON object : View

Products Affected

joinmastodon

mastodon

CWE

CWE-601

URL Redirection to Untrusted Site ('Open Redirect')

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