CVE-2023-27351
CVE-2023-27351 is a security flaw in PaperCut NG/MF, printing software offices and schools use. Attackers can get into PaperCut NG/MF without a valid password. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 20 Apr 2026, and says ransomware gangs have used it.[1]
PaperCut NG/MF is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. PaperCut has published a fix or advice.
Description
CISA calls it an improper authentication in PaperCut NG/MF. In its words: “PaperCut NG/MF contains an improper authentication vulnerability that could allow remote attackers to bypass authentication on affected installations via the SecurityRequestFilter class.”[1]
The CVE record adds: “This vulnerability allows remote attackers to bypass authentication on affected installations of PaperCut NG 22.0.5 (Build 63914). Authentication is not required to exploit this vulnerability. The specific flaw exists within the SecurityRequestFilter class. The issue results from improper implementation of the authentication algorithm. An attacker can leverage this vulnerability to bypass authentication on the system. Was ZDI-CAN-19226.”[2]
The underlying weakness is improper authentication (CWE-287), in MITRE’s list of common software weaknesses.
It scores 7.5 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; PaperCut’s advisory has them[3]. CISA names the product as PaperCut NG/MF.
Most families won’t have PaperCut NG/MF; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 20 Apr 2026, 1,096 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 4 May 2026 to fix it.[1] CISA says ransomware gangs have used it.
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 78%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
PaperCut has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[1]
- Check whether you use it.PaperCut NG/MF is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 4 May 2026 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 7.5.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 78%.[4] |
See also
Other PaperCut NG/MF flaws
- CVE-2026-82078: unsafe reflection ·
- CVE-2026-81578: missing authentication for critical function ·
- CVE-2023-2533: cross-site request forgery (CSRF) ·
Other PaperCut flaws
- CVE-2023-27350, PaperCut MF/NG: improper access control ·
Other improper authentication flaws
- CVE-2026-105133, AhsayCBS: improper authentication ·
- CVE-2026-42018, JFrog Artifactory: improper authentication ·
- CVE-2026-82329, JFrog Artifactory: improper authentication ·
- CVE-2026-59822, BerriAI LiteLLM: improper authentication ·
- CVE-2023-49105, ownCloud: improper authentication ·
Added the same day
- CVE-2026-20133, Cisco Catalyst SD-WAN Manager: exposure of sensitive information to an unauthorized actor ·
- CVE-2026-20128, Cisco Catalyst SD-WAN Manager: storing passwords in a recoverable format ·
- CVE-2026-20122, Cisco Catalyst SD-WAN Manger: catalyst SD-WAN manager incorrect use of privileged APIs ·
- CVE-2025-48700, Synacor Zimbra Collaboration Suite (ZCS): cross-site scripting ·
- CVE-2025-32975, Quest KACE Systems Management Appliance (SMA): improper authentication ·
Every PaperCut flaw on CISA’s list · Everything added in April 2026
References
- ^ Cybersecurity and Infrastructure Security Agency. “PaperCut NG/MF Improper Authentication Vulnerability”. Known Exploited Vulnerabilities Catalog, added 20 Apr 2026.
- ^ National Institute of Standards and Technology. “CVE-2023-27351 Detail”. National Vulnerability Database, published 20 Apr 2023.
- ^ PaperCut. Advisories and fixes: papercut.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.781, percentile 99.6, 31 Oct 2026.
- CVE Program. “CVE-2023-27351”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.