CVE-2015-3245
Description
It was found that libuser, as used by the chfn userhelper functionality, did not properly filter out newline characters in GECOS fields. A local, authenticated user could use this flaw to corrupt the /etc/passwd file, resulting in a denial-of-service on the system.
Statement
Red Hat Enterprise Linux 5 is now in Production 3 Phase of the support and maintenance life cycle. This vulnerability has been rated as having Moderate security impact and is not currently planned to be addressed in future updates. For additional information, refer to the Red Hat Enterprise Linux Life Cycle: https://access.redhat.com/support/policy/updates/errata/.
Mitigation
Add pam_warn and pam_deny rules to /etc/pam.d/chfn and /etc/pam.d/chsh to prevent non-root users from using this functionality. With these edits, the files should contain:
#%PAM-1.0
auth sufficient pam_rootok.so
auth required pam_warn.so
auth required pam_deny.so
auth include system-auth
account include system-auth
password include system-auth
session include system-auth
Afterwards, attempts by unprivileged users to use chfn and chsh (and the respective functionality in the userhelper program) will fail, and will be logged (by default in /var/log/secure).
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v2 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 1.7 | 2.1 | N/A |
| Attack Vector | Local | Local | N/A |
| Access Complexity | Low | Low | N/A |
| Authentication | Single | None | N/A |
| Confidentiality Impact | None | None | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | Partial | Partial | N/A |
Vector
Red Hat: AV:L/AC:L/Au:S/C:N/I:N/A:P
NVD: AV:L/AC:L/Au:N/C:N/I:N/A:P
Understanding the Weakness (CWE)
Confidentiality,Integrity,Availability,Other
Technical Impact: Execute Unauthorized Code or Commands; Alter Execution Logic; DoS: Crash, Exit, or Restart
Acknowledgements
Red Hat would like to thank Qualys for reporting this issue.
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