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Fencer Intel
critical 9.8

CVE-2026-63438 json

2FAuth: Reverse Proxy Guard Auto-Creates Users With Admin Promotion From Unauthenticated Header Value

published 4mo ago modified yesterday also EUVD-2026-118491 , GHSA-r9xx-45m8-mw24

Unreviewed: the maintainers' own advisory

Published by the maintainers on their GitHub repository Bubka/2FAuth. GitHub has not reviewed it into the GitHub Advisory Database, so the affected packages and versions are the maintainers' word. Read the full advisory on GitHub.

cvss
9.8
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 43%
public exploits
0
none known

Summary

2FAuth is a web app to manage Two-Factor Authentication (2FA) accounts and generate their security codes. Prior to 8.0.0, when AUTHENTICATION_GUARD=reverse-proxy-guard accepts authentication headers from a client that did not pass through a trusted proxy, RemoteUserProvider::retrieveById() creates an account for an unknown REMOTE_USER, promotes the first created account to administrator, and synchronizes the account email from the configured mail header. An unauthenticated remote client can therefore create an administrator on a fresh instance or impersonate and redirect email for a known account, exposing 2FA secrets and administrative functions. This issue is fixed in version 8.0.0.

Patch / fix

  • 2fauth 2fauth 8.0.0

Is CVE-2026-63438 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
total
Assessed
yesterday

Exploit prediction

0.51% chance of exploitation in the next 30 days, higher than 43% of all scored CVEs (FIRST EPSS, 2026-11-11).

Exploits and checks

  • github.com https://github.com/Bubka/2FAuth/security/advisories/GHSA-r9xx-45m8-mw24 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Bubka 2FAuth

Classification

Weakness

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of Bubka/2FAuth published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.