CVE-2026-33868Network attack vector

Unauthenticated open redirect via encoded path segments

Published Mar 27, 2026 · Updated Mar 27, 2026

Open redirect in Mastodon release branches before 4.3.21, 4.4.15, and 4.5.8 allows remote attackers to redirect visitors. The /web/* route accepts URL-encoded slashes that bypass Rails path normalization and treats the resulting path as a host-relative external redirect. Exploitation requires a visitor to follow the crafted URL; the redirect supports phishing, credential harvesting, or OAuth authorization-code interception.

CVSS severity4.3
Medium
EPSS probability0.47%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Open redirect in Mastodon release branches before 4.3.21, 4.4.15, and 4.5.8 allows remote attackers to redirect visitors. The /web/* route accepts URL-encoded slashes that bypass Rails path normalization and treats the resulting path as a host-relative external redirect. Exploitation requires a visitor to follow the crafted URL; the redirect supports phishing, credential harvesting, or OAuth authorization-code interception.

The record

CVE
CVE-2026-33868
Published
Mar 27, 2026
Updated
Mar 27, 2026
Vendor
Mastodon
Product
Mastodon
Classifications
CWE-601, T1566.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 27, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 27, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 4.3.21
  2. Affected versionversion=>= 4.4.0, < 4.4.15
  3. Affected versionversion=>= 4.5.0, < 4.5.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mastodon · Mastodonversion=< 4.3.21; version=>= 4.4.0, < 4.4.15; version=>= 4.5.0, < 4.5.8

Published CVSS scores

6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-601URL Redirection to Untrusted Site ('Open Redirect')
T1566.002Spearphishing Link

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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