PaperCut Zero-Day Under Active Attack: Emergency Patch Released
PaperCut warns that a zero-day in NG and MF print management products is being actively exploited, shipping emergency patches with no CVE assigned yet.
PaperCut Software confirmed active exploitation of a zero-day affecting PaperCut NG and MF, with confirmed customer incidents, and released emergency patches on Friday ahead of technical details or a CVE assignment. The company urges customers to restrict web access to trusted IP addresses, disconnect application servers from the internet, and watch for indicators including tampered or truncated server.log files, database error strings, and suspicious activity involving pc-app.exe. The article recalls the May 2023 exploitation of CVE-2023-27350 and CVE-2023-27351 by the financially motivated Lace Tempest group, a Clop ransomware RaaS affiliate, though no attacker attribution has been given for the current campaign.
- Active zero-day exploitation of PaperCut NG/MF with confirmed customer incidents; no CVE yet assigned.
- Emergency patches released; PaperCut urges restricting web interfaces to trusted IPs or disconnecting from the internet.
- Attackers may delete, truncate or alter server.log files; database error strings and pc-app.exe activity serve as IoCs.
- In 2023, Lace Tempest, a Clop RaaS affiliate, exploited PaperCut flaws CVE-2023-27350 and CVE-2023-27351.
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… |
Full article461 words · extracted from securityaffairs.com · click to collapse
PaperCut warns that a zero-day in NG and MF is being exploited. The company already release emergency patches to address it.
PaperCut Software warns that attackers are actively exploiting a zero-day in its NG and MF print management products. The flaw has no CVE yet, and the company has not released technical details.
PaperCut issued emergency patches on Friday and urged customers to install them immediately. It also recommends disconnecting application servers from the internet and limiting access to trusted IP addresses.
“If your PaperCut NG/MF Application Server is accessible from the public internet, immediately restrict web access to trusted IP addresses only (e.g. internal IP addresses).” states the advisory. “Use firewall rules, network access controls, or equivalent measures to ensure the PaperCut server’s web interfaces cannot be reached from untrusted internet addresses. Take this action now, even if you have not observed suspicious activity.”
The company confirmed incidents affecting customers and said its investigation is still underway.
“PaperCut Software security response team is investigating active exploitation of a vulnerability affecting PaperCut NG and PaperCut MF.” reads the advisory. “We are aware of confirmed customer incidents and are treating this matter with the highest priority. Our investigation is ongoing. We will update this security bulletin as verified information becomes available, including indicators of compromise and remediation guidance.”
PaperCut has not yet disclosed details about the vulnerability, the attack method, or the attackers behind the campaign.
So far, the company has identified several indicators of compromise:
- Intrusion-detection, endpoint-security, or network-monitoring tools may flag suspicious activity involving the PaperCut Application Server, especially activity linked to
pc-app.exe. - Attackers may delete, truncate, or alter PaperCut
server.logfiles to hide their activity. - The
server.logfile may contain these entries:ERROR No suitable driver found for jdbc:no:xERROR DatabaseUtils - Database error looking up cardID: VALUES CAST
Users running PaperCut should check their systems for these signs of compromise.
In May 2023, Microsoft warned that Iran-linked APT groups were exploiting another flaw, tracked as CVE-2023-27350, in attacks against PaperCut MF/NG print management servers. The CVE-2023-27350 flaw 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.
In April 2023, Microsoft linked the attacks exploiting the CVE-2023-27350 and CVE-2023-27351 vulnerabilities in print management software PaperCut to a financially motivated threat actor tracked as Lace Tempest (formerly DEV-0950). The group is known to be an affiliate of the Clop ransomware RaaS affiliate, it has been linked to GoAnywhere attacks and Raspberry Robin infection. Since April 13, 2023, Lace Tempest added the PaperCut exploits to its arsenal.
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