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CVE-2026-33868

MEDIUMCVSS 6.1/10EPSS 0.52%

Last modified

CVE-2026-33868 is a medium-severity vulnerability rated 6.1/10 on the CVSS scale. 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. EPSS estimates a 0.52% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1
6.1/10

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

EPSS Probability
0.52%

39.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
JoinmastodonMastodon< 4.3.21
JoinmastodonMastodon>= 4.4.0, < 4.4.15
JoinmastodonMastodon>= 4.5.0, < 4.5.8

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is 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.
How severe is CVE-2026-33868?
CVE-2026-33868 has a CVSS score of 6.1/10 (MEDIUM severity). The EPSS model estimates a 0.52% probability of exploitation in the next 30 days.
How do I fix CVE-2026-33868?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-33868?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST