CVE-2026-33868

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 v3 4.3 MEDIUM

4.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact NONE

Integrity Impact LOW

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/mastodon/mastodon/security/advisories/GHSA-xqw8-4j56-5hj6	Vendor Advisory

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:joinmastodon:mastodon::::::::
	cpe:2.3:a:joinmastodon:mastodon::::::::
	cpe:2.3:a:joinmastodon:mastodon::::::::

History

30 Mar 2026, 19:14

Type	Values Removed	Values Added
References	~~() https://github.com/mastodon/mastodon/security/advisories/GHSA-xqw8-4j56-5hj6 -~~	() https://github.com/mastodon/mastodon/security/advisories/GHSA-xqw8-4j56-5hj6 - Vendor Advisory
CPE		cpe:2.3:a:joinmastodon:mastodon::::::::
First Time		Joinmastodon Joinmastodon mastodon

Information

Published : 2026-03-27 20:16

Updated : 2026-03-30 19:14

NVD link : CVE-2026-33868

Mitre link : CVE-2026-33868

CVE.ORG link : CVE-2026-33868

JSON object : View

Products Affected

joinmastodon

mastodon

CWE

CWE-601

URL Redirection to Untrusted Site ('Open Redirect')

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