CVE-2026-33868 json
Mastodon has a GET-Based Open Redirect via '/web/%2F<domain>'
published 2026-03-27 7 mo ago modified 2026-09-08 2 mo ago also BIT-mastodon-2026-33868 , EUVD-2026-16783 , GHSA-xqw8-4j56-5hj6
- cvss
- 4.3
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.5%
- EPSS 0.5% chance of exploitation in 30 days, percentile 41%
- public exploits
- 0
- none known, plus a Nuclei check
Summary
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.
Patch / fix
- bitnami mastodon 4.3.21, 4.4.15, 4.5.8
- joinmastodon mastodon 4.3.21, 4.4.15, 4.5.8
CISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 7 mo ago
Exploit prediction
0.47% chance of exploitation in the next 30 days, higher than 41% of all scored CVEs (FIRST EPSS, 2026-11-08).
Exploits and checks
- Nuclei template Mastodon - Open Redirect nuclei detection template
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 4.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N |
| NVD | 3.1 | 6.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N |
| OSV | 3.1 | 6.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| bitnami | mastodon | <4.3.21 >=4.4.0, <4.4.15 >=4.5.0, <4.5.8 |
4.3.21 4.4.15 4.5.8 |
Affected products
- mastodon mastodon
Classification
- Weakness
-
- CWE-601 URL Redirection to Untrusted Site
References
-
github.com
/mastodon/mastodon/security/advisories/GHSA-xqw8-4j56-5hj6
vendor-advisory, advisory
-
nvd.nist.gov
/vuln/detail/CVE-2026-33868
web
Sources
- CVE List CVE-2026-33868
- NVD CVE-2026-33868
- OSV BIT-mastodon-2026-33868
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