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Critical Linux Kernel Vulnerability
Critical security bug has been discovered in the Linux kernel within do_brk() function that may lead to full compromise of vulnerable system. Successful exploitation of do_brk() leads to full compromise of vulnerable system, including gaining full uid 0 privileges... EnGarde Secure Linux is not vulnerable to this exploit and no update is necessary. Other vendors are expected to publish updates shortly.. . .
Critical security bug has been discovered in the Linux kernel within do_brk() function that may lead to full compromise of vulnerable system. Successful exploitation of do_brk() leads to full compromise of vulnerable system, including gaining full uid 0 privileges... EnGarde Secure Linux is not vulnerable to this exploit and no update is necessary. Other vendors are expected to publish updates shortly.
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Synopsis: Linux kernel do_brk() lacks argument bound checking Product: Linux Version: up to 2.4.23, others Vendor: https://www.kernel.org/ URL: https://isec.pl/vulnerabilities/isec-0012-do_brk.txt CVE: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0961 Author: Paul Starzetz
Wojciech Purczynski Date: December 1, 2003 Issue: ====== Critical security bug has been discovered in the Linux kernel within do_brk() function that may lead to full compromise of vulnerable system. Details: ======== The physical memory of a x86 machine running one of the recent Linux kernels is managed in a simplified flat memory model. Each user process may address a memory ranging from 0 up to TASK_SIZE bytes. Memory above this limit is not accessible to the user and contains kernel code with its data structures. User process is divided into logical sections, called virtual memory areas. The kernel keeps tracks and manages user process's virtual memory areas to provide proper memory management and memory protection faults handling. More details of Linux memory management are out of the scope of this article and can be found in . The do_brk() is an internal kernel function that is called indirectly to manage process's memory heap (brk), growing or shrinking it accordingly. It is simplified version of mmap(2) system call that only handles anonymous mappings (i.e. not initialized data). The function lacks of bound checks of its parameters and may be exploited to create arbitrary large virtual memory area, exceeding user accessible memory limit. Thus, the kernel memory above this limit may become part of user process's memory as visible to the kernel memory manager. Typical memory layout of user process may look like: bash$ cat /proc/self/maps 08048000-0804c000 r-xp 00000000 03:02 207935 /bin/cat 0804c000-0804d000 rw-p 00003000 03:02 207935 /bin/cat 0804d000-0804e000 rwxp 00000000 00:00 0 40000000-40015000 r-xp 00000000 03:02 207495 /lib/ld-2.3.2.so 40015000-40016000 rw-p 00014000 03:02 207495 /lib/ld-2.3.2.so 40016000-40017000 rw-p 00000000 00:00 0 40020000-40021000 rw-p 00000000 00:00 0 42000000-4212f000 r-xp 00000000 03:02 319985 /lib/tls/libc-2.3.2.so 4212f000-42132000 rw-p 0012f000 03:02 319985 /lib/tls/libc-2.3.2.so 42132000-42134000 rw-p 00000000 00:00 0 bfffe000-c0000000 rwxp fffff000 00:00 0 The do_brk() function is called from within ELF and a.out loaders as well as from brk(2) syscall. These are three different vectors which may be used to exploit do_brk() bug. After successful exploitation process memory may contain a large memory mapping, i.e.: 080a5000-c891d000 rwxp 00000000 00:00 0 Impact: ======= Successful exploitation of do_brk() leads to full compromise of vulnerable system, including gaining full uid 0 privileges, possibility of kernel code and data structures modification as well as kernel-level (ring0) code execution. Tested and successfully exploited kernel versions include: o 2.4.20-18.9 as shipped with Red Hat 9.0 o 2.4.22 (vanila) o 2.4.22 with grsecurity patch There is no known reliable workaround for this vulnerability except. We recommend upgrading to the most recent kernel version (so far the 2.4.23 kernel) on all vulnerable systems. Limiting maximum size of user process's data segment with ulimit -d command provides some workaround for exploit based on brk system call. However, there are at least two other attack vectors that can not be disabled without patching the system. We have succesfully created proof-of-concept exploit. Unfortunately we guess that our exploit may have leaked to the underground. Credits: ======== Paul Starzetz has indenpendently discovered the bug, Wojciech Purczynski invented and provided numerous techniques to automatically and efficiently exploit the bug. References: ===========  Intel Architecture Software Developer's Manual Volume 2 "Instruction Set Reference"  Intel Architecture Software Developer's Manual Volume 3 "System Programming Guide"  Daniel P. Bovet, Marco Cesati, "Understanding the Linux Kernel" - -- Paul Starzetz iSEC Security Research https://isec.pl/ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.7 (GNU/Linux) iD8DBQE/y8jRC+8U3Z5wpu4RAnHvAKDEC0/e5xr7s61wMSsr4XUDl5+S8ACfQTqe CsfpNtUMoLW7xDS22JSAJP0= =dpRp -----END PGP SIGNATURE-----