Description
Proxmox Virtual Environment (VE) 7.0 through 8.0 contains an authentication bypass vulnerability in libpve-access-control before 8.0.4 that allows unauthenticated attackers to authenticate as any existing enabled user without a configured second factor by supplying an arbitrary tfa-challenge value in the API login endpoint. Attackers can send a POST request to the access ticket API endpoint with any value in the tfa-challenge parameter to completely skip password verification, gaining unauthorized access including to the root@pam account. All affected releases are end of life.
Published: 2026-09-01
Score: 9.3 Critical
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

An unauthenticated attacker can supply any value for the tfa‑challenge parameter to the Proxmox VE login API, causing the system to skip password verification. This vulnerability, mapped to CWE‑304, enables the attacker to authenticate as any active user, including the root@pam account, thereby granting full control of the host.

Affected Systems

All Proxmox Virtual Environment releases from version 7.0 through 8.0, prior to the 8.0.4 update. Every affected build has reached end‑of‑life and receives no further security updates.

Risk and Exploitability

The CVSS score of 9.3 reflects a critical severity. The EPSS score is not available, and the vulnerability is not listed in the CISA KEV catalog, but the lack of authentication and the ability to remotely send the HTTP POST request make the vulnerability highly exploitable from any network location that can reach the API endpoint.

Generated by OpenCVE AI on September 1, 2026 at 23:22 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade Proxmox VE to version 8.0.4 or newer to obtain the fixed libpve‑access‑control component.
  • Apply network controls such as a firewall rule or network segmentation to restrict external access to the API ticket endpoint until the upgrade is performed.
  • If upgrade cannot be performed immediately, disable the tfa‑challenge parameter or remove two‑factor authentication for the API to prevent the bypass until a patch is available.

Generated by OpenCVE AI on September 1, 2026 at 23:22 UTC.

Tracking

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Advisories

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History

Tue, 01 Sep 2026 22:00:00 +0000

Type Values Removed Values Added
Description Proxmox Virtual Environment (VE) 7.0 through 8.0 contains an authentication bypass vulnerability in libpve-access-control before 8.0.4 that allows unauthenticated attackers to authenticate as any existing enabled user without a configured second factor by supplying an arbitrary tfa-challenge value in the API login endpoint. Attackers can send a POST request to the access ticket API endpoint with any value in the tfa-challenge parameter to completely skip password verification, gaining unauthorized access including to the root@pam account. All affected releases are end of life.
Title Proxmox VE 7.0-8.0 Authentication Bypass via tfa-challenge Parameter
Weaknesses CWE-304
References
Metrics cvssV3_1

{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}

cvssV4_0

{'score': 9.3, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N'}

Subscriptions

No data.

cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-09-01T21:59:53.698Z

Reserved: 2026-09-01T21:23:55.860Z

Link: CVE-2023-54391

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-01T22:17:10.283

Modified: 2026-09-01T22:17:10.283

Link: CVE-2023-54391

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-01T23:30:05Z

Weaknesses
  • CWE-304

    Missing Critical Step in Authentication