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9.8Critical

CVE-2023-54391

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.

What this means for your business

  • An attacker can use it remotely, over a network, without a login, and without anyone at your company clicking anything.
  • FIRST's prediction model gives it a 2% chance of attack attempts being seen in the next 30 days, ranking above 76% of all known flaws.

What to do

  1. 1Ask your IT team or provider whether any of your systems use the affected product.
  2. 2If you do, follow the vendor's guidance. No patch reference has been published yet.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

Check if you’re exposedBook a call

Scoring

CVSS
9.8 (v3.1)
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS v4
9.3
Weakness
CWE-304
Assigned by
disclosure@vulncheck.com

Dates

Published
2026-09-01
Last modified
2026-09-08
Sources
NVD

References