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Fencer Intel
critical 9.8

CVE-2026-63439 json

2FAuth: Reverse Proxy Guard Trusts Client-Supplied Headers Without Proxy Verification

published 4mo ago modified 2d ago also EUVD-2026-118492 , GHSA-mh8r-74x2-r457

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
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 35%
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 is enabled, ReverseProxyGuard::user() reads the default REMOTE_USER identity header, or a custom identity header selected by the AUTH_PROXY_HEADER_FOR_USER configuration setting, without confirming that the request originated from a configured trusted proxy. A remote client that can reach the application directly can forge the selected identity header and authenticate as an existing user, including an administrator, gaining access to stored 2FA secrets and account or application management functions. This issue is fixed in version 8.0.0.

Patch / fix

  • 2fauth 2fauth 8.0.0

Is CVE-2026-63439 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
2d ago

Exploit prediction

0.41% chance of exploitation in the next 30 days, higher than 35% of all scored CVEs (FIRST EPSS, 2026-11-11).

Exploits and checks

  • github.com https://github.com/Bubka/2FAuth/security/advisories/GHSA-mh8r-74x2-r457 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.