2FAuth: Reverse Proxy Guard Auto-Creates Users With Admin Promotion From Unauthenticated Header Value
Affects 2FAuth before 8.0.0 when AUTHENTICATION_GUARD is set to reverse-proxy-guard and the app is reachable without a properly configured reverse proxy. Fixed in 8.0.0.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 8.0.0
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 8.0.0.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 27/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
2FAuth, a web app for managing two-factor authentication accounts and generating their security codes, is affected when its reverse-proxy authentication guard accepts headers from clients that did not come through the trusted proxy. An unauthenticated attacker on the network can exploit this remotely, without logging in, to create or take over accounts, including administrator access that exposes 2FA secrets.
Read the original description
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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed, reachable over the network without a login · Unknown: Advisories don't say whether default setups are affected
- Reach?/20Unknown. No tracked technology or package matched
- Severity9.8/10CVSS 9.8
- No patch0/5No signal
What would change the score
- Would score about 72 if added to CISA KEV
- Would score about 67 if CISA's SSVC rates exploitation active
- Would score about 32 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 8.0.0.
Timeline
- CVE published
- First seen by cve.now
- Posted on X by cve.now
Affected versions
- Bubka 2FAuth
fixed in 8.0.0
Evidence 5
- Advisory
- Repository
- Repository
- Repository
- Repository
Corrections
None so far.
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Questions about CVE-2026-63438
Is CVE-2026-63438 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
The reverse proxy guard accepts a header value without authenticating it, which lets an unauthenticated request auto-create a user account and promote it to administrator. The attacker can then gain full control of the instance.Source: github.com
Which versions are affected by CVE-2026-63438?
2FAuth: before 8.0.0.Source: cve.now feed data
Am I affected, and how do I check?
Versions before 8.0.0 are affected when AUTHENTICATION_GUARD is set to reverse-proxy-guard and the application is directly reachable without a properly configured reverse proxy. Admin promotion through auto-creation additionally requires an instance with zero existing users, such as a fresh deployment. To check, look at the AUTHENTICATION_GUARD setting in the configuration and the installed version.Source: github.com
How do I fix CVE-2026-63438?
Upgrade 2FAuth to version 8.0.0 or later, which contains the fix.Source: github.com