Title: FreeBSD exec() Inherited Signal Handler Vulnerability
Severity: HIGH
Description:
On UNIX systems, fork() is the method by which a new process is created. The fork() system call causes a duplicate of the calling process to be created called a 'child' process.
Once created, a child process may replace it's image with that of a binary executable on the file system using the exec() system call.
The rfork() system call allows the calling process to specify explicitly which resources the child process is to inherit from the parent. Among those resources are signal handlers.
A vulnerability exists in the FreeBSD exec() implementation. The system call fails to prevent signal handlers from being inherited by processes attempting to exec setuid images. As a result, setuid processes may end up with user-supplied signal handlers set.
This can lead to arbitrary code execution. An attacker may be able to place instructions in the environment and set the signal handler to their address.
When the setuid process catches the signal associated with the handler, the arbitrary code in the environment will be executed.
It may be possible to elevate privileges by exploiting this vulnerability.
Affected Products:
- FreeBSD FreeBSD 4.0.0
- FreeBSD FreeBSD 4.1.0
- FreeBSD FreeBSD 4.2.0
- FreeBSD FreeBSD 4.3.0
References:
- FreeBSD: FreeBSD Security Information
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