Instituto Nacional de ciberseguridad. Sección Incibe
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CVE-2026-33868

Severity CVSS v4.0:
Pending analysis
Type:
CWE-601 URL Redirection to Untrusted Site ('Open Redirect')
Publication date:
27/03/2026
Last modified:
30/03/2026

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.

Impact

Vector 3.x
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N CVSS v3.1 Severity and Metrics:

Base Score: 4.30 MEDIUM
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Attack Vector (AV): Network
Attack Complexity (AC): Low
Privileges Required (PR): None
User Interaction (UI): Required
Scope (S): Unchanged
Confidentiality (C): None
Integrity (I): Low
Availability (A): None

Base Score 3.x
4.30
Severity 3.x
MEDIUM

Vulnerable products and versions

CPE From Up to
cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:* 4.3.21 (excluding)
cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:* 4.4.0 (including) 4.4.15 (excluding)
cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:* 4.5.0 (including) 4.5.8 (excluding)

To consult the complete list of CPE names with products and versions, see this page


References to Advisories, Solutions, and Tools