J-Security Center

Title: Linux-PAM Pam_Wheel Module getlogin() Username Spoofing Privileged Escalation Vulnerability

Severity: MODERATE

Description:

Linux-PAM (Pluggable Authentication Modules for Linux) is an authentication system used to enforce various access restrictions and security mechanisms. The pam_wheel module can be used to enforce access restrictions to various utilities, such as 'su', using the 'wheel' group.

When the "trust" configuration option is implemented, users of the trusted group are not required to supply a password when running the 'su' utility. A configuration option "use_uid" is also available which specifies whether a user of the trusted group should be verified using the login name or user id.

A vulnerability has been discovered in the pam_wheel module when running a configuration with the "trust" option enabled and the "use_uid" option disabled. The vulnerability occurs due to the insecure use of the getlogin() function when verifying user login names against a list of trusted users. It should be noted that the said configuration is not used by default.

Due to the insecure use of getlogin() a local attacker may be capable of gaining unauthorized 'root' privileges without supplying a password. This can be accomplished by spoofing the 'logname' return value, effectively making the getlogin() function to return a value of another logged in user. The spoofed user would have to be logged in to the system and also be part of the trusted group for this to attack take place.

Successful exploitation of this issue would allow an attacker to invoke the 'su' utility and gain unauthorized superuser privileges.

Affected Products:

  • Linux-PAM Linux-PAM 0.77.0
  • RedHat Advanced Workstation for the Itanium Processor 2.1.0
  • RedHat Advanced Workstation for the Itanium Processor 2.1.0 IA64
  • RedHat Enterprise Linux AS 2.1
  • RedHat Enterprise Linux AS 2.1 IA64
  • RedHat Enterprise Linux ES 2.1
  • RedHat Enterprise Linux ES 2.1 IA64
  • RedHat Enterprise Linux WS 2.1
  • RedHat Enterprise Linux WS 2.1 IA64
  • RedHat Linux 7.3.0 i386
  • RedHat Linux 9.0.0 i386

References:

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