Computer security researchers are again warning about a critical vulnerability in the Linux kernel that could be used by malicious hackers to take control of systems using the popular open source operating system.ISEC Security Research said Monday that it found a\u00a0critical vulnerability\u00a0in code that is used to manage virtual memory on Linux systems. The vulnerability affects versions of the Linux kernel up to and including version 2.6 and would give low-level Linux users total control over a Linux system.ISEC, a noncommercial security research group based in Poland, discovered the problem in kernel code for a component called "mremap," according to a message posted by Paul Starzetz, an iSEC member.The kernel is the core of the Linux operating system and provides basic services for all other parts of the operating system such as allocating processor time for the programs running on the computer and managing the system's memory or storage.Mremap provides functionality for managing virtual memory and is used continuously by programs that have exhausted their allocation of memory, or that have been allocated memory in excess of what they need, according to Dave Wreski, chief executive officer of secure Linux vendor Guardian Digital.Attackers could use the vulnerability to create an invalid virtual memory area (VMA), which could destabilize the Linux operating system or allow a malicious user to run attack code on the system. Attackers would need local user access to the vulnerable machine, but would not need any special privileges on the Linux system to exploit the hole, iSEC said.Researchers at iSEC said they have developed test code to exploit the mremap vulnerability.However, taking advantage of the hole will be more difficult for outsiders, who will need to get user access to the machine they want to compromise and then work backwards from the Linux kernel patches to spot the flaw and write code to exploit it, Wreski said.The warning follows news in December of another critical flaw in version 2.4 of the Linux kernel. Malicious hackers used that vulnerability to attack servers belonging to The Debian Project, which produces the noncommercial Debian Linux distribution.Critical Linux kernel vulnerabilities are rare and the disclosure of two such holes within weeks of each other is unprecedented, Wreski said.The increase in the number of critical flaws may be the result of more groups scrutinizing the security of the Linux source code, he said.ISEC did a good job of coordinating with Linux vendors, working with them for a month prior to publishing information on the mremap vulnerability, Wreski said.Guardian Digital and Red Hat\u00a0released updated kernel packages on Monday to fix the mremap security hole. ISEC encouraged Linux users to fix vulnerable systems as soon as software patches became available from their vendor.