CVE-2023-27350: PaperCut MF/NG Improper Access Control Vulnerability

What it is

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 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. Was ZDI-CAN-18987.

Exploitation evidence

First exploit evidence seen: 2023-03-13 (earliest date across the sources below).

Exploited in the wild

• CISA KEV: listed since 2023-04-21. Source

Public exploit code

Metasploit

• exploit/multi/http/papercut_ng_auth_bypass: PaperCut PaperCutNG Authentication Bypass (disclosure 2023-03-13)

Exploit-DB

• EDB-51391: PaperCut NG/MG 22.0.4 - Authentication Bypass (2023-04-25)
• EDB-51452: PaperCut NG/MG 22.0.4 - Remote Code Execution (RCE) (2023-05-23)

GitHub proof-of-concept repositories

14 public repositories from 14 accounts, first seen 2023-04-21. Most starred: horizon3ai/CVE-2023-27350 (57 stars), view repository.

Verify before running: public PoCs can be malicious. Read the code and only run it in an isolated lab. A PoC means exploit code is public, not that this CVE is exploited in the wild.

Sources: CISA KEV · Rapid7 Metasploit Framework module metadata · Exploit-DB (OffSec) · nomi-sec/PoC-in-GitHub.

How to fix it

CISA required action

Apply updates per vendor instructions. (source: CISA KEV)

Fixed versions

• papercut papercut mf: upgrade to 20.1.7 or later (affected from 8.0)
• papercut papercut mf: upgrade to 21.2.11 or later (affected from 21.0.0)
• papercut papercut mf: upgrade to 22.0.9 or later (affected from 22.0.0)
• papercut papercut ng: upgrade to 20.1.7 or later (affected from 8.0)
• papercut papercut ng: upgrade to 21.2.11 or later (affected from 21.0.0)
• papercut papercut ng: upgrade to 22.0.9 or later (affected from 22.0.0)

Derived from the NVD CPE configuration (versionEndExcluding / versionEndIncluding). Always confirm with the vendor advisory.

Vendor advisories and patches

• https://www.papercut.com/kb/Main/PO-1216-and-PO-1219 (CISA KEV notes)

MITRE ATT&CK mitigations for this chain

• M1048 Application Isolation and Sandboxing (for T1190) : Application isolation will limit what other processes and system features the exploited target can access.
• M1037 Filter Network Traffic (for T1190, T1105) : Restrict outbound network traffic from public-facing servers to prevent unauthorized connections from initiating communications with attacker-controlled infrastructure. While this may not prevent the initial exploitation, it limits the attacker's ability to verify and control the compromised server post-exploit, reduci
• M1030 Network Segmentation (for T1190) : Segment externally facing servers and services from the rest of the network with a DMZ or on separate hosting infrastructure.
• M1016 Vulnerability Scanning (for T1190) : Regularly scan externally facing systems for vulnerabilities and establish procedures to rapidly patch systems when critical vulnerabilities are discovered through scanning and through public disclosure.
• M1026 Privileged Account Management (for T1190, T1059) : Use least privilege for service accounts will limit what permissions the exploited process gets on the rest of the system.
• M1050 Exploit Protection (for T1190) : Web Application Firewalls may be used to limit exposure of applications to prevent exploit traffic from reaching the application.
• M1035 Limit Access to Resource Over Network (for T1190) : Ensure that all publicly exposed services are actually intended to be so, and restrict access to any that should only be available internally.
• M1051 Update Software (for T1190) : Update software regularly by employing patch management for externally exposed applications.
• M1033 Limit Software Installation (for T1059) : Prevent user installation of unrequired command and scripting interpreters.
• M1045 Code Signing (for T1059) : Where possible, only permit execution of signed scripts.

Detection Generic guidance

• Initial Access: Alert on unusual requests to the affected service (odd paths, oversized payloads, exploit strings) in WAF, reverse-proxy and application logs.
• Execution: Watch for the service process spawning shells or script interpreters (cmd.exe, powershell, sh, bash, python) via EDR process-tree rules.
• Command and Control: Alert on outbound connections from the server to new or rare destinations.

Response checklist Generic guidance

1. Inventory: find every instance of the affected product and version (include internet-facing and forgotten ones).
2. Patch or mitigate per the vendor advisory; if you cannot patch, remove internet exposure or apply the vendor workaround.
3. Assume compromise if the system was exposed before patching: hunt for the indicators in the advisory and review logs back to the disclosure date.
4. Rotate credentials and secrets stored on or used by the affected system if compromise cannot be ruled out.