CVE•Published 2026-03-27•1 article on news•5 live references•NVD data

CVE-2026-33868

Vulnerability data via CVEDB (Shodan)

CVSS v3.1

4.3

MEDIUM

EPSS percentile

Exploit Prediction Scoring System · top 60% of all CVEs

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.

Timeline

Published 2026-03-27

External references

NVD MITRE Exploit-DB Sploitus VulnCheck

Search for exposed instances

Shodan + Censys queries derived from NVD's CPE data. The vuln tag catches assets Shodan has explicitly linked to this CVE; the product / banner fingerprints find exposed instances even when the vuln tag was never applied (which is common).

Shodan · vuln tag50 hosts

vuln:CVE-2026-33868

Hosts Shodan has explicitly fingerprinted as vulnerable.

Shodan · product

product:"Joinmastodon Mastodon"

All exposed Joinmastodon Mastodon instances — cross-reference with the CVE's affected-version range.

Shodan · banner/body mention

http.html:"Mastodon"

HTTP body or banner mentions "Mastodon" — catches deploys Shodan didn't identify as a product.

More intel sources (5)

Shodan report

vuln:CVE-2026-33868