CVE-2023-29383
LowCVSS 3.3Exploitation Probability (EPSS)
Low risk35th percentile - higher than 35% of all known CVEs
Summary
In Shadow 4.13, it is possible to inject control characters into fields provided to the SUID program chfn (change finger). Although it is not possible to exploit this directly (e.g., adding a new user fails because \n is in the block list), it is possible to misrepresent the /etc/passwd file when viewed. Use of \r manipulations and Unicode characters to work around blocking of the ':' character make it possible to give the impression that a new user has been added.
Risk Assessment
An adversary may be able to convince a system administrator to take the system offline (an indirect, social-engineered denial of service) by demonstrating that 'cat /etc/passwd' shows a rogue user account.
Recommendation
Update Shadow to a patched version and verify /etc/passwd contents using tools resistant to control characters instead of direct cat.
Other vulnerabilities in Shadow
See all- CVE-2016-6252High
Integer overflow in shadow 4.2.1 allows local users to gain privileges via crafted input to newuidmap.
- CVE-2017-12424Critical
In the newusers tool in shadow before version 4.5, there is a possibility to manipulate internal data structures in ways unintended by the authors. Malformed input may lead to crashes (with a buffer overflow or other memory corruption) or other unspecified behaviors.
- CVE-2013-4235Medium
shadow: TOCTOU (time-of-check time-of-use) race condition when copying and removing directory trees.
Original NVD description (English source)
In Shadow 4.13, it is possible to inject control characters into fields provided to the SUID program chfn (change finger). Although it is not possible to exploit this directly (e.g., adding a new user fails because \n is in the block list), it is possible to misrepresent the /etc/passwd file when viewed. Use of \r manipulations and Unicode characters to work around blocking of the : character make it possible to give the impression that a new user has been added. In other words, an adversary may be able to convince a system administrator to take the system offline (an indirect, social-engineered denial of service) by demonstrating that "cat /etc/passwd" shows a rogue user account.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS