CVE-2009-0361 in pam-krb5
Summary
by MITRE
Russ Allbery pam-krb5 before 3.13, as used by libpam-heimdal, su in Solaris 10, and other software, does not properly handle calls to pam_setcred when running setuid, which allows local users to overwrite and change the ownership of arbitrary files by setting the KRB5CCNAME environment variable, and then launching a setuid application that performs certain pam_setcred operations.
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Analysis
by VulDB Data Team • 08/27/2019
The vulnerability described in CVE-2009-0361 represents a critical privilege escalation flaw within the pam-krb5 module version 3.12 and earlier, affecting numerous Unix-like systems including Solaris 10. This issue stems from improper handling of PAM credential management operations when executing setuid programs, creating a pathway for local attackers to manipulate file ownership and potentially gain elevated system privileges. The vulnerability specifically manifests when the pam_setcred function is invoked within setuid contexts, allowing malicious actors to exploit the Kerberos credential cache environment variable KRB5CCNAME to overwrite arbitrary files and change their ownership.
The technical root cause of this vulnerability lies in the pam-krb5 module's failure to properly validate or sanitize the KRB5CCNAME environment variable during credential setting operations. When a setuid application executes pam_setcred, the module incorrectly processes the Kerberos credential cache location, enabling attackers to manipulate the credential cache file path through environment variable manipulation. This flaw operates under CWE-276, which classifies improper file permissions and access control mechanisms, and specifically relates to CWE-73, which deals with external control of file name or path. The vulnerability creates a condition where the setuid application's credential handling logic becomes susceptible to environment variable injection, allowing for arbitrary file manipulation.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential system compromise and data integrity violations. Local attackers can leverage this flaw to overwrite system files, modify critical configuration data, or manipulate file ownership to gain persistent access to system resources. The attack vector is particularly concerning because it requires minimal privileges and can be executed through standard user accounts, making it an attractive target for both casual attackers and more sophisticated threat actors. The vulnerability affects systems where PAM modules handle Kerberos authentication, particularly those using libpam-heimdal and the Solaris 10 su command, which are commonly deployed in enterprise environments and critical infrastructure systems.
Mitigation strategies for this vulnerability require immediate patching of affected pam-krb5 modules to version 3.13 or later, which addresses the improper credential handling through enhanced environment variable validation and proper file access controls. System administrators should also implement monitoring of setuid applications and their PAM module usage to detect anomalous credential handling patterns. The remediation process should include verifying that KRB5CCNAME environment variables are properly sanitized before credential operations and ensuring that setuid applications perform adequate input validation. Additionally, organizations should consider implementing privilege separation techniques and reviewing access controls for Kerberos credential cache files to prevent unauthorized manipulation. This vulnerability aligns with ATT&CK technique T1068, which covers privilege escalation through local exploitation, and demonstrates the importance of proper environment variable handling in security-critical system components. The fix essentially closes the gap in PAM module implementation that allowed attackers to bypass normal file access controls through credential cache manipulation.