VulnerabilityAnalyzed

CVE-2026-33868

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.

MEDIUM 6.1EPSS 0.47%

Does this matter?

Lower severity and a low EPSS score (0.47%). Track it; it rarely justifies an emergency change on its own.

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 3.1: 6.1 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
EPSS: 0.47% probability · 40th percentile
CISA KEV: Not listed
Weakness: CWE-601
Affected: joinmastodon/mastodon
Source: security-advisories@github.com

References

https://github.com/mastodon/mastodon/security/advisories/GHSA-xqw8-4j56-5hj6Vendor Advisory

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.