CVE-2021-41194Network attack vector

Account takeover via inconsistent username normalization

Published Oct 28, 2021 · Updated Aug 4, 2024

Improper access control in JupyterHub First Use Authenticator before 1.0.0 allows remote attackers to access guessed user accounts. The authenticator stores passwords under unnormalized usernames while JupyterHub normalizes usernames, so a case variant can set a second password for the same account. The attack requires create_users=True and a known or guessed username, granting the attacker's password access to that user's files.

CVSS severity9.1
Critical
EPSS probability1.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in JupyterHub First Use Authenticator before 1.0.0 allows remote attackers to access guessed user accounts. The authenticator stores passwords under unnormalized usernames while JupyterHub normalizes usernames, so a case variant can set a second password for the same account. The attack requires create_users=True and a known or guessed username, granting the attacker's password access to that user's files.

The record

CVE
CVE-2021-41194
Published
Oct 28, 2021
Updated
Aug 4, 2024
Vendor
JupyterHub
Product
JupyterHub First Use Authenticator
Classifications
CWE-284, T1078
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 28, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record 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=< 1.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

JupyterHub · JupyterHub First Use Authenticatorversion=< 1.0.0

Published CVSS scores

9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.1GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
6.8NVDAV:N/AC:M/Au:N/C:P/I:P/A:P

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.

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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-284Improper Access Control
T1078Valid Accounts

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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