Experts released PoC for actively exploited PaperCut flaw
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2023-27350 | Authentication Bypass Leading to SYSTEM RCE in PaperCut MF/NG PaperCut MF and PaperCut NG print management software contain an improper access control flaw (CWE-284) in the SetupCompleted class that allows an unauthenticated attacker to bypass authentication and reach internal administrative functionality. The flaw is triggered by sending crafted, unauthenticated requests to the PaperCut application's web interface, without requiring valid user credentials. A successful attacker gains the ability to execute code in the context of the SYSTEM account on the PaperCut server, typically a Windows print server, giving full control of that host. Any organization running PaperCut MF or NG is potentially affected, and exposure is highest where the server's web interface is reachable from the internet or by untrusted networks. Exploitation is confirmed in the wild: CISA added the flaw to the KEV on 2023-04-21 with known ransomware use, and EPSS rates exploitation probability at 100% within 30 days. Do: Apply the vendor's updates as instructed (this is the required action in CISA KEV) — upgrade PaperCut MF/NG to the patched releases listed in PaperCut's security advisory rather than relying on unpatched installs. Until patched, restrict network access to the PaperCut web/admin interface so it is reachable only from trusted hosts, and check the server for signs of compromise given known ransomware use. Prioritize internet-facing PaperCut servers, which public scans show are exposed in the thousands. | 9.8 | 100% | KEV ransomware PoC ×3 |
| masstens of thousands of organizations (~70k+) and millions of users; thousands of internet-exposed PaperCut servers | |
| CVE-2023-27351 | Authentication Bypass in PaperCut NG/MF Print Management Software CVE-2023-27351 is an improper authentication flaw (CWE-287) in the SecurityRequestFilter class of PaperCut NG and MF print management software, where the authentication algorithm is improperly implemented. A remote, unauthenticated attacker can trigger it over the network with no user interaction or special privileges to bypass authentication on the affected server (CVSS 3.1: 7.5). Once authentication is bypassed, the attacker gains access to the PaperCut system; in observed campaigns this access was leveraged to deliver Cl0p and LockBit ransomware, as confirmed by Microsoft. Organizations running PaperCut NG (version 22.0.5, Build 63914, is cited in the advisory) or PaperCut MF are affected. The flaw was exploited as a zero-day, is CISA KEV-listed (added 2026-04-20) with known ransomware use, and EPSS places the 30-day exploitation probability at 78.1%. Do: Upgrade PaperCut NG/MF to the fixed release per the vendor's emergency patch advisory, first confirming the running build (NG 22.0.5, Build 63914, is cited as affected). Restrict internet-facing access to PaperCut servers and hunt for signs of post-exploitation, given confirmed use to deliver Cl0p and LockBit ransomware. US federal agencies must apply mitigations per CISA BOD 22-01 (or vendor instructions) or discontinue use of the product if mitigations are unavailable. | 7.5 | 78% | KEV ransomware |
| large≈75,000+ sites/organizations (PaperCut NG/MF is deployed at tens of thousands of organizations; public scans have found thousands of servers directly… |
Indicators of compromiseauto-extracted · verify before use · export allAll →
| Type | Indicator | Context |
|---|---|---|
| domain | windowservicecemter.com | d that the domain hosting the tools employed in the attack, windowservicecemter[.]com, was registered on April 12, 2023. It is interesting to n |
Full article644 words · extracted from securityaffairs.com · click to collapse
Threat actors are exploiting PaperCut MF/NG print management software flaws in attacks in the wild, while researchers released PoC exploit code.
Hackers are actively exploiting PaperCut MF/NG print management software flaws (tracked as CVE-2023-27350 and CVE-2023-27351) in attacks in the wild.
The threat actors were observed installing the Atera remote management software to take over vulnerable servers.
On April 19th, Print management software provider PaperCut confirmed that it is aware of the active exploitation of the CVE-2023-27350 vulnerability.
The company received two vulnerability reports from the cybersecurity firm Trend Micro for high/critical severity security issues in PaperCut MF/NG. Trend Micro announced they will disclose further information (TBD) about the vulnerability on 10th May 2023.
The company addressed both vulnerabilities with the release of PaperCut MF and PaperCut NG versions 20.1.7, 21.2.11 and 22.0.9 and later, it highly recommends upgrading to one of these versions containing the fix
“We have evidence to suggest that unpatched servers are being exploited in the wild.” reads the advisory published by PaperCut. “PaperCut received our first report from a customer of suspicious activity on their PaperCut server on the 18th April at 03:30 AEST / 17th April 17:30 UTC. PaperCut has conducted analysis on all customer reports, and the earliest signature of suspicious activity on a customer server potentially linked to this vulnerability is 14th April 01:29 AEST / 13th April 15:29 UTC.”
The CVE-2023-27350 (CVSS score – 9.8) is a PaperCut MF/NG Improper Access Control Vulnerability. PaperCut MF/NG contains an improper access control vulnerability within the SetupCompleted class that allows authentication bypass and code execution in the context of system.
The cybersecurity firm Horizon3 disclosed details of the flaw along with a PoC exploit code for CVE-2023-27350. The PoC code allows attackers to bypass authentication and execute code on vulnerable PaperCut servers.
“The specific flaw exists within the SetupCompleted class. The issue results from improper access control. An attacker can leverage this vulnerability to bypass authentication and execute arbitrary code in the context of SYSTEM.” reads the post published by Horizon3. “Comparing the vulnerable SetupCompleted class from v19.2.7 to the patched version in v21.2.11 with Meld, we see that if setup has already been completed, visiting this page will now redirect to the “Home” page – eliminating the session puzzling logic flaw.
Confirming the authentication bypass in the GUI, we browse to the page at http://10.0.40.56:9191/app?service=page/SetupComplete and click “Login”.
The experts published the full proof-of-concept exploit on GitHub.
“This POC uses an authentication bypass vulnerability chained with abuse of builtin scripting functionality to execute code.” reads the description on GitHub.
Horizon3 researchers also shared Indicators of Compromise (IoCs) for the attacks exploiting PaperCut issues.
Huntress researchers have observed post-exploitation activities within its partner environments after attackers exploited the above PaperCut MF/NG vulnerabilities.
Huntress security researcher Caleb Stewart also devised a proof-of-concept exploit for these threats, below is the video PoC shared by the company:
“From our recreated proof-of-concept, we observed child processes spawned underneath the pc-app.exe process. The screenshot below showcases a simple test of invoking PowerShell to call out to another location, demonstrating the achieved code execution.” reads the report published by Huntress.”
The researchers noticed that the domain hosting the tools employed in the attack, windowservicecemter[.]com, was registered on April 12, 2023. It is interesting to note that the domain was also hosting malware a variant of the TrueBot malware.
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