Is CVE-2026-33868 in the CISA KEV catalog?

No. CVE-2026-33868 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-33868?

CVE-2026-33868 has a CVSS v3 base score of 4.3 (MEDIUM).

What is the EPSS score for CVE-2026-33868?

CVE-2026-33868 has an EPSS score of 0.52% (40th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-33868?

Upgrade mastodon to 4.5.8 or later.

CVE & CISA-KEV Catalog

CVE-2026-33868

MEDIUM

4.3

CVSS v3

NVD

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.

CWE-601Open Redirect

How to fix

Remediation Available

mastodonNVD

Affected:>= 4.5.0, < 4.5.8Fixed in:4.5.8CVE-2026-33868derived from NVD

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionRequired

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityLow

AvailabilityNone

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

Exploit Intelligence

0.52%probability of exploitation in 30 days

40thpercentile

Moderate risk: more likely to be exploited than 40% of all known CVEs.

References

Vendor Advisory1

github.com

Related Vulnerabilities

Other CWE-601 (Open Redirect) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2025-4123	High	7.6	98%	-	Fix
CVE-2018-11784	Medium	4.3	94%	-	Fix
CVE-2021-22881	Medium	6.1	87%	-	Fix
CVE-2022-45402	Medium	6.1	82%	-	Fix
CVE-2017-1000117	High	8.8	78%	-	Fix
CVE-2019-10098	Medium	6.1	74%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-03-30.