CVE-2023-29383 is a vulnerability identified in the Shadow suite version 4.13, specifically involving the SUID program chfn, which is used to change user finger information. The vulnerability arises because chfn improperly handles control characters injected into its input fields. While direct exploitation to add unauthorized users is prevented by blocking newline characters (\n), attackers can circumvent restrictions on the colon character (:) by using Unicode characters and carriage return (\r) manipulations. This allows them to craft entries that, when the /etc/passwd file is viewed (e.g., via 'cat /etc/passwd'), appear to show rogue user accounts that do not actually exist. This is a form of display manipulation rather than a direct compromise of system integrity. The primary risk is social engineering: convincing system administrators that the system has been compromised, potentially leading to unnecessary system downtime or offline status as a precaution. The vulnerability is classified under CWE-125 (Out-of-bounds Read), indicating improper handling of input data. No patches or exploits are currently documented, and no CVSS score has been assigned. The vulnerability affects Unix-like systems using Shadow 4.13 with the vulnerable chfn binary installed with SUID privileges. The attack requires local access to run chfn and inject the crafted input, but no elevated privileges are needed beyond what chfn allows. User interaction is not required beyond the attacker executing the command. The scope is limited to systems where chfn is present and accessible. This vulnerability does not allow direct privilege escalation or unauthorized account creation but can cause operational disruption through social engineering denial of service.

For European organizations, the primary impact of CVE-2023-29383 is operational disruption rather than direct compromise. Organizations relying on Unix-like systems with Shadow 4.13 and the vulnerable chfn program may be susceptible to attackers manipulating the /etc/passwd file display to falsely indicate unauthorized user accounts. This can lead to loss of trust in system integrity, triggering precautionary measures such as taking critical systems offline or initiating costly incident response procedures. Such downtime can affect business continuity, especially in sectors dependent on high availability like finance, healthcare, and critical infrastructure. The indirect denial of service caused by social engineering may also erode confidence in system administration processes. Since no direct privilege escalation or data breach occurs, confidentiality and integrity impacts are minimal. However, availability is affected through potential unnecessary system outages. The threat is more pronounced in environments where system administrators rely heavily on manual inspection of /etc/passwd for user account verification and where automated integrity monitoring is lacking. Given the lack of known exploits, the immediate risk is low but could increase if attackers develop reliable exploitation techniques. European organizations with strict uptime requirements and regulatory obligations around system availability should be particularly cautious.

To mitigate CVE-2023-29383, European organizations should implement several targeted measures beyond generic advice: 1) Restrict access to the chfn SUID binary by limiting execution permissions to trusted users only, reducing the attack surface. 2) Employ integrity monitoring tools that verify the actual content and structure of /etc/passwd beyond simple text display, detecting manipulation attempts. 3) Educate system administrators about this specific vulnerability and the possibility of display-based deception to prevent social engineering-induced downtime. 4) Implement automated user account management and auditing tools that do not rely solely on manual inspection of /etc/passwd, reducing human error. 5) Monitor logs for unusual chfn usage patterns that could indicate exploitation attempts. 6) When available, apply official patches or updates from the Shadow suite maintainers addressing this vulnerability. 7) Consider deploying mandatory access controls (e.g., SELinux, AppArmor) to restrict chfn behavior further. 8) Establish incident response protocols that verify suspicious user account reports through multiple methods before taking systems offline. These steps collectively reduce the risk of exploitation and minimize operational impact.