CVSS 3.1
9.8 criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HCVE-2026-63439
Critical (9.8) in bubka 2fauth. EPSS 0.4% estimated probability of exploitation activity in the next 30 days.
On this page
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.
Severity
- EPSS
- 0.4% estimated probability of exploitation activity in the next 30 days; 35th percentile. Scored 2026-11-10. A forecast for this CVE across the internet, not for your own systems.
- CISA's assessment (SSVC)
- Exploitation: PoC · Automatable: yes · Technical impact: total, assessed 2026-11-09. From CISA's Vulnrichment in the CVE List: whether it is exploited, whether exploiting it can be automated, and how much control it gives.
- CWE
- CWE-287 Improper Authentication
- OWASP Top 10
- A07:2025 Authentication Failures
- Published
- Modified
- NVD analysis
- Awaiting analysis
- Record from
- the NVD, synced
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Explain CVE-2026-63439 for an engineer deciding whether to act. Use https://cve.bz/api/public/cves/CVE-2026-63439?via=ask-ai-copy and https://cve.bz/cve/CVE-2026-63439?via=ask-ai-copy as the source of truth: what is affected and which versions fix it, whether it is in CISA KEV, public exploits, and its EPSS (an internet-wide 30-day estimate of exploitation activity, not a forecast for my systems). If they give no fixed versions, use the CVE record https://cveawg.mitre.org/api/cve/CVE-2026-63439 or the vendor advisory, not third-party mirrors. Tell me how to check whether I am affected and how to verify a fix. Cite the sources and say where they are uncertain.Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this CVE's id and public links.
Affected
Versions
From the CNA's record in the CVE List.
| Product | Affected |
|---|---|
| Bubka 2FAuth | < 8.0.0 |
Attack patterns (CAPEC)
- CAPEC-22 Exploiting Trust in Client Likelihood: High · Severity: High
- CAPEC-57 Utilizing REST's Trust in the System Resource to Obtain Sensitive Data Likelihood: Medium · Severity: Very High
- CAPEC-94 Adversary in the Middle (AiTM) Likelihood: High · Severity: Very High
- CAPEC-114 Authentication Abuse Severity: Medium
- CAPEC-115 Authentication Bypass Severity: Medium
- CAPEC-151 Identity Spoofing Likelihood: Medium · Severity: Medium
- CAPEC-194 Fake the Source of Data Severity: Medium
- CAPEC-593 Session Hijacking Likelihood: High · Severity: Very High
- CAPEC-633 Token Impersonation Severity: Medium
- CAPEC-650 Upload a Web Shell to a Web Server Severity: High
The attack patterns MITRE's CAPEC relates to this record's weaknesses, as MITRE names them. Credits.