User redirection to attacker-controlled sites via login links
Published Apr 3, 2026 · Updated Apr 3, 2026
Open redirect in JupyterHub before 5.4.4 allows remote attackers to send users to an attacker-controlled site through a crafted login link. The login redirect flow accepts an attacker-selected post-login destination that bypasses JupyterHub's external-site check and emits it in the Location header. Exploitation requires a user to click the link and complete the login flow; the resulting redirect can support phishing, with no reported service interruption.
Summary
What happened
Open redirect in JupyterHub before 5.4.4 allows remote attackers to send users to an attacker-controlled site through a crafted login link. The login redirect flow accepts an attacker-selected post-login destination that bypasses JupyterHub's external-site check and emits it in the Location header. Exploitation requires a user to click the link and complete the login flow; the resulting redirect can support phishing, with no reported service interruption.
The record
- CVE
- CVE-2026-33709
- Published
- Apr 3, 2026
- Updated
- Apr 3, 2026
- Vendor
- Project Jupyter
- Product
- JupyterHub
- Classifications
- CWE-601, T1566.002
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 3, 2026CVE publishedPublication date reported by the CVE source.
- Apr 3, 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.
- Affected versionversion=< 5.4.4
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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