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.
Weakness
The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Shadow | Shadow_project | 4.13 (including) | 4.13 (including) |
| Shadow | Ubuntu | bionic | * |
| Shadow | Ubuntu | esm-infra-legacy/trusty | * |
| Shadow | Ubuntu | esm-infra/bionic | * |
| Shadow | Ubuntu | esm-infra/focal | * |
| Shadow | Ubuntu | esm-infra/xenial | * |
| Shadow | Ubuntu | focal | * |
| Shadow | Ubuntu | jammy | * |
| Shadow | Ubuntu | kinetic | * |
| Shadow | Ubuntu | lunar | * |
| Shadow | Ubuntu | mantic | * |
| Shadow | Ubuntu | trusty | * |
| Shadow | Ubuntu | trusty/esm | * |
| Shadow | Ubuntu | upstream | * |
| Shadow | Ubuntu | xenial | * |
Potential Mitigations
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/10.html
- https://cwe.mitre.org/data/definitions/101.html
- https://cwe.mitre.org/data/definitions/105.html
- https://cwe.mitre.org/data/definitions/108.html
- https://cwe.mitre.org/data/definitions/120.html
- https://cwe.mitre.org/data/definitions/13.html
- https://cwe.mitre.org/data/definitions/135.html
- https://cwe.mitre.org/data/definitions/14.html
- https://cwe.mitre.org/data/definitions/24.html
- https://cwe.mitre.org/data/definitions/250.html
- https://cwe.mitre.org/data/definitions/267.html
- https://cwe.mitre.org/data/definitions/273.html
- https://cwe.mitre.org/data/definitions/28.html
- https://cwe.mitre.org/data/definitions/3.html
- https://cwe.mitre.org/data/definitions/34.html
- https://cwe.mitre.org/data/definitions/42.html
- https://cwe.mitre.org/data/definitions/43.html
- https://cwe.mitre.org/data/definitions/45.html
- https://cwe.mitre.org/data/definitions/46.html
- https://cwe.mitre.org/data/definitions/47.html
- https://cwe.mitre.org/data/definitions/51.html
- https://cwe.mitre.org/data/definitions/52.html
- https://cwe.mitre.org/data/definitions/53.html
- https://cwe.mitre.org/data/definitions/6.html
- https://cwe.mitre.org/data/definitions/64.html
- https://cwe.mitre.org/data/definitions/67.html
- https://cwe.mitre.org/data/definitions/7.html
- https://cwe.mitre.org/data/definitions/71.html
- https://cwe.mitre.org/data/definitions/72.html
- https://cwe.mitre.org/data/definitions/76.html
- https://cwe.mitre.org/data/definitions/78.html
- https://cwe.mitre.org/data/definitions/79.html
- https://cwe.mitre.org/data/definitions/8.html
- https://cwe.mitre.org/data/definitions/80.html
- https://cwe.mitre.org/data/definitions/83.html
- https://cwe.mitre.org/data/definitions/84.html
- https://cwe.mitre.org/data/definitions/9.html
References
- https://github.com/shadow-maint/shadow/commit/e5905c4b84d4fb90aefcd96ee618411ebfac663d
- https://github.com/shadow-maint/shadow/pull/687
- https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/cve-2023-29383-abusing-linux-chfn-to-misrepresent-etc-passwd/
- https://www.trustwave.com/en-us/resources/security-resources/security-advisories/?fid=31797
- https://github.com/shadow-maint/shadow/commit/e5905c4b84d4fb90aefcd96ee618411ebfac663d
- https://github.com/shadow-maint/shadow/pull/687
- https://lists.debian.org/debian-lts-announce/2025/04/msg00026.html
- https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/cve-2023-29383-abusing-linux-chfn-to-misrepresent-etc-passwd/
- https://www.trustwave.com/en-us/resources/security-resources/security-advisories/?fid=31797