CVE-2023-27351 PaperCut NG/MF: login or permission bypass
In plain words: A door that should be locked is not: part of the system can be reached without a valid login or permission. The attacker gets in as a user or administrator without knowing a password.
Confirmed exploited by CISA on · US federal patch deadline May 4, 2026
What to do
- Install PaperCut's security update for NG/MF. If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Keep a list of every internet-facing server you run so nothing is forgotten.
- Patch anything in this catalog first, ahead of normal patch cycles.
- Put admin and file-transfer apps behind a VPN or single sign-on instead of the open internet.
Who is affected
Work IT. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.
What's at risk: Mass data theft and ransomware: a single flaw in a file-transfer or email server has exposed thousands of organisations at once.
The details
- Official name
- PaperCut NG/MF Improper Authentication Vulnerability
- Product
- PaperCut NG/MF
- CISA description
- PaperCut NG/MF contains an improper authentication vulnerability that could allow remote attackers to bypass authentication on affected installations via the SecurityRequestFilter class.
- Type of flaw
- Login or permission bypass (CWE-287)
- Confirmed exploited
- Apr 20, 2026 — known to be used in ransomware attacks
- US federal patch deadline
- May 4, 2026
Ask Cleus about it
Ask about a vulnerability, an update, a weird message, or the news. Plain-word answers, free, no account.
Answering about CVE-2023-27351 ·
Questions about CVE-2023-27351
Is CVE-2023-27351 being exploited?
Yes. CISA added CVE-2023-27351 to its Known Exploited Vulnerabilities catalog on Apr 20, 2026, which means there is reliable evidence of real-world attacks, including by ransomware groups.
How do I fix CVE-2023-27351?
Install PaperCut's security update for NG/MF. If no update exists, follow the vendor's workaround or stop using the product until one ships. Keep a list of every internet-facing server you run so nothing is forgotten.
Am I affected by CVE-2023-27351?
Only if you use PaperCut NG/MF. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.