Open Redirect Vulnerability in Mastodon Social Network Server
CVE-2026-33868

4.3MEDIUM

Key Information:

Vendor

Mastodon

Status
Mastodon
Vendor
CVE Published:
27 March 2026

What is CVE-2026-33868?

An open redirect vulnerability is present in the Mastodon social network server due to improper handling of URL-encoded path segments in the /web/* route. Attackers can exploit this weakness by crafting maliciously encoded URLs, which may redirect users to arbitrary external domains, facilitating phishing attacks and potential theft of OAuth credentials. This vulnerability arises because URL-encoded slashes bypass the normalization process in Rails, allowing host-relative redirects. Users of Mastodon should update to the patched versions 4.5.8, 4.4.15, or 4.3.21 to mitigate the risk.

Affected Version(s)

mastodon >= 4.5.0, < 4.5.8 < 4.5.0, 4.5.8

mastodon >= 4.4.0, < 4.4.15 < 4.4.0, 4.4.15

mastodon < 4.3.21 < 4.3.21

References

https://github.com/mastodon/mastodon/security/advisories/...
x_refsource_CONFIRM

CVSS V3.1

Score:
4.3
Severity:
MEDIUM
Confidentiality:
None
Integrity:
Low
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
Required
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

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