2FAuth: Reverse Proxy Guard Trusts Client-Supplied Headers Without Proxy Verification
Only affects 2FAuth 7.0.1 and earlier when AUTHENTICATION_GUARD is set to reverse-proxy-guard. The vendor has no separate rating, and the fix is 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
- Specific setups only
Do first: Check whether your setup matches what the bug needs. AUTHENTICATION_GUARD is set to reverse-proxy-guard The application is reachable directly by the attacker, bypassing a properly configured reverse proxy that strips or overwrites the authentication header Affected versions are 7.0.1 and earlier
- 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? →
- 22/100 · 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? →
- Specific setups only
- 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 mode is enabled. A remote attacker who can reach the application directly, without logging in, can forge the identity header to sign in as an existing user, including an administrator, and gain access to stored 2FA secrets and account management functions.
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 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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure12/25Specific setups only, reachable over the network without a login
- 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
What to do
Check whether your setup matches what the bug needs.
AUTHENTICATION_GUARD is set to reverse-proxy-guard The application is reachable directly by the attacker, bypassing a properly configured reverse proxy that strips or overwrites the authentication header Affected versions are 7.0.1 and earlierUpgrade 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 3
- Advisory
- Repository
- Repository
Corrections
None so far.
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Questions about CVE-2026-63439
Is CVE-2026-63439 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 the identity header sent by the client without checking that it came through the proxy. A request that reaches the application directly can therefore forge that header and sign in as any existing user, including an administrator.Source: github.com
Which versions are affected by CVE-2026-63439?
2FAuth: before 8.0.0.Source: cve.now feed data
Am I affected, and how do I check?
Versions 7.0.1 and earlier are affected, but only when AUTHENTICATION_GUARD is set to reverse-proxy-guard. The application must also be reachable directly, without a properly configured reverse proxy that strips or overwrites the authentication header. To check, look at the AUTHENTICATION_GUARD value in the configuration and at the installed version.Source: github.com
How do I fix CVE-2026-63439?
Upgrade 2FAuth to version 8.0.0 or later, which is the listed fixed version.Source: github.com