This article was originally published on the Red Hat Customer Portal. The information may no longer be current.
Update 2014-09-30 19:30 UTC
Questions have arisen around whether Red Hat products are vulnerable to CVE-2014-6277 and CVE-2014-6278. We have determined that RHSA-2014:1306, RHSA-2014:1311, and RHSA-2014:1312 successfully mitigate the vulnerability and no additional actions need to be taken.
Update 2014-09-26 12:00 UTC
We have written a FAQ to address some of the more common questions seen regarding the recent bash issues.
Frequently Asked Questions about the Shellshock Bash flaws
Update 2014-09-26 02:20 UTC
Red Hat has released patched versions of Bash that fix CVE-2014-7169. Information regarding these updates can be found in the errata. All customers are strongly encouraged to apply the update as this flaw is being actively attacked in the wild.
Fedora has also released a patched version of Bash that fixes CVE-2014-7169. Additional information can be found on Fedora Magazine.
Update 2014-09-25 16:00 UTC
Red Hat is aware that the patch for CVE-2014-6271 is incomplete. An attacker can provide specially-crafted environment variables containing arbitrary commands that will be executed on vulnerable systems under certain conditions. The new issue has been assigned CVE-2014-7169.
We are working on patches in conjunction with the upstream developers as a critical priority. For details on a workaround, please see the knowledgebase article.
Red Hat advises customers to upgrade to the version of Bash which contains the fix for CVE-2014-6271 and not wait for the patch which fixes CVE-2014-7169. CVE-2014-7169 is a less severe issue and patches for it are being worked on.
Bash or the Bourne again shell, is a UNIX like shell, which is perhaps one of the most installed utilities on any Linux system. From its creation in 1980, Bash has evolved from a simple terminal based command interpreter to many other fancy uses.
In Linux, environment variables provide a way to influence the behavior of software on the system. They typically consists of a name which has a value assigned to it. The same is true of the Bash shell. It is common for a lot of programs to run Bash shell in the background. It is often used to provide a shell to a remote user (via ssh, telnet, for example), provide a parser for CGI scripts (Apache, etc) or even provide limited command execution support (git, etc)
Coming back to the topic, the vulnerability arises from the fact that you can create environment variables with specially-crafted values before calling the Bash shell. These variables can contain code, which gets executed as soon as the shell is invoked. The name of these crafted variables does not matter, only their contents. As a result, this vulnerability is exposed in many contexts, for example:
-
ForceCommand is used in sshd configs to provide limited command execution capabilities for remote users. This flaw can be used to bypass that and provide arbitrary command execution. Some Git and Subversion deployments use such restricted shells. Regular use of OpenSSH is not affected because users already have shell access.
-
Apache server using mod_cgi or mod_cgid are affected if CGI scripts are either written in Bash, or spawn subshells. Such subshells are implicitly used by system/popen in C, by os.system/os.popen in Python, system/exec in PHP (when run in CGI mode), and open/system in Perl if a shell is used (which depends on the command string).
-
PHP scripts executed with mod_php are not affected even if they spawn subshells.
-
DHCP clients invoke shell scripts to configure the system, with values taken from a potentially malicious server. This would allow arbitrary commands to be run, typically as root, on the DHCP client machine.
-
Various daemons and SUID/privileged programs may execute shell scripts with environment variable values set / influenced by the user, which would allow for arbitrary commands to be run.
-
Any other application which is hooked onto a shell or runs a shell script as using Bash as the interpreter. Shell scripts which do not export variables are not vulnerable to this issue, even if they process untrusted content and store it in (unexported) shell variables and open subshells.
Like "real" programming languages, Bash has functions, though in a somewhat limited implementation, and it is possible to put these Bash functions into environment variables. This flaw is triggered when extra code is added to the end of these function definitions (inside the enivronment variable). Something like:
$ env x='() { :;}; echo vulnerable' bash -c "echo this is a test" vulnerable this is a test
The patch used to fix this flaw, ensures that no code is allowed after the end of a Bash function. So if you run the above example with the patched version of Bash, you should get an output similar to:
$ env x='() { :;}; echo vulnerable' bash -c "echo this is a test" bash: warning: x: ignoring function definition attempt bash: error importing function definition for `x' this is a test
We believe this should not affect any backward compatibility. This would, of course, affect any scripts which try to use environment variables created in the way as described above, but doing so should be considered a bad programming practice.
Red Hat has issued security advisories that fixes this issue for Red Hat Enterprise Linux. Fedora has also shipped packages that fixes this issue.
We have additional information regarding specific Red Hat products affected by this issue that can be found at https://access.redhat.com/site/solutions/1207723
Information on CentOS can be found at http://lists.centos.org/pipermail/centos/2014-September/146099.html.
저자 소개
Red Hat is the world’s leading provider of enterprise open source software solutions, using a community-powered approach to deliver reliable and high-performing Linux, hybrid cloud, container, and Kubernetes technologies.
Red Hat helps customers integrate new and existing IT applications, develop cloud-native applications, standardize on our industry-leading operating system, and automate, secure, and manage complex environments. Award-winning support, training, and consulting services make Red Hat a trusted adviser to the Fortune 500. As a strategic partner to cloud providers, system integrators, application vendors, customers, and open source communities, Red Hat can help organizations prepare for the digital future.
유사한 검색 결과
채널별 검색
오토메이션
기술, 팀, 인프라를 위한 IT 자동화 최신 동향
인공지능
고객이 어디서나 AI 워크로드를 실행할 수 있도록 지원하는 플랫폼 업데이트
오픈 하이브리드 클라우드
하이브리드 클라우드로 더욱 유연한 미래를 구축하는 방법을 알아보세요
보안
환경과 기술 전반에 걸쳐 리스크를 감소하는 방법에 대한 최신 정보
엣지 컴퓨팅
엣지에서의 운영을 단순화하는 플랫폼 업데이트
인프라
세계적으로 인정받은 기업용 Linux 플랫폼에 대한 최신 정보
애플리케이션
복잡한 애플리케이션에 대한 솔루션 더 보기
오리지널 쇼
엔터프라이즈 기술 분야의 제작자와 리더가 전하는 흥미로운 스토리
제품
- Red Hat Enterprise Linux
- Red Hat OpenShift Enterprise
- Red Hat Ansible Automation Platform
- 클라우드 서비스
- 모든 제품 보기
툴
체험, 구매 & 영업
커뮤니케이션
Red Hat 소개
Red Hat은 Linux, 클라우드, 컨테이너, 쿠버네티스 등을 포함한 글로벌 엔터프라이즈 오픈소스 솔루션 공급업체입니다. Red Hat은 코어 데이터센터에서 네트워크 엣지에 이르기까지 다양한 플랫폼과 환경에서 기업의 업무 편의성을 높여 주는 강화된 기능의 솔루션을 제공합니다.