NG - Authentication Bypass (CVE-2023-27351)

CVE-2023-27351 is an authentication bypass vulnerability in PaperCut NG 22.0.5, allowing remote attackers to gain unauthorized access to the system without valid credentials. Exploiting a flaw in the SecurityRequestFilter class, attackers can circumvent authentication mechanisms, potentially exposing sensitive information and administrative functions to unauthorized users.

CrowdSec has been tracking this vulnerability and its exploits since 14th of January 2026.

Insights from the CrowdSec network reveal that the attackers trying to exploit CVE-2023-27351 are composed of a fairly even mix of opportunistic and targeted actors. Some attackers employ preliminary reconnaissance, while others use indiscriminate scanning. CrowdSec data also reveals a clear uptick in attacks involving CVE-2023-27351 over the past week. Activity is above the usual baseline, suggesting growing attention from attackers. This may reflect rising awareness, recent exploit releases, or expanded targeting efforts.

Attackers exploit this vulnerability by sending crafted POST requests to endpoints such as /rpc/api/rest/master/user/createInternalUser;/keepalive and /rpc/api/rest/master/user/getExportedUser;/keepalive, bypassing authentication controls to create and access internal user accounts.