CVE-2026-33868

MEDIUM

4.3

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.

CVE Details

CVSS v3.1 Score4.3

SeverityMEDIUM

CVSS VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Attack VectorNETWORK

ComplexityLOW

Privileges RequiredNONE

User InteractionREQUIRED

Published3/27/2026

Last Modified3/30/2026

Sourcenvd

Honeypot Sightings0

Affected Products

joinmastodon:mastodon

Weaknesses (CWE)

CWE-601

References

https://github.com/mastodon/mastodon/security/advisories/GHSA-xqw8-4j56-5hj6(security-advisories@github.com)

IOC Correlations

No correlations recorded

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