CVE-2014-6271 쉘쇼크 Bash 취약점 조치

✔️ CentOS 5 + bash 3.2, CentOS 6 + bash 4.1.2, CentOS 7 + bash 4.2.45에서 테스트하였습니다.

1 개요

shellshock

[CVE-2014-6271] GNU Bash 원격코드 인젝션 취약점 확인 및 조치

2014년 9월 Bourne Again Shell(Bash) 취약점 보안 업데이트

쉘쇼크, 셸쇼크, 쉘쇼크 해결방법, 조치방법

• CentOS 6: bash-4.1.2-15.el6_4.x86_64 → bash-4.1.2-15.el6_5.2.x86_64
• CentOS 7: bash-4.2.45-5.el7.x86_64 → bash-4.2.45-5.el7_0.4.x86_64

2 확인방법

env x='() { :;}; echo vulnerable' bash -c "echo this is a test"

rm -f echo; env X='() { (a)=>\' sh -c "echo date"; cat echo

(for x in {1..200} ; do echo "for x$x in ; do :"; done; for x in {1..200} ; do echo done ; done) | bash ||
echo "CVE-2014-7187 vulnerable, word_lineno"

3 확인 1 (취약)

[root@jmnote ~]# env x='() { :;}; echo vulnerable' bash -c "echo this is a test"
vulnerable
this is a test

→ echo vulnerable이 수행되었으므로 취약함

[root@jmnote ~]# rm -f echo; env X='() { (a)=>\' sh -c "echo date"; cat echo
sh: X: line 1: syntax error near unexpected token `='
sh: X: line 1: `'
sh: error importing function definition for `X'

→ date 명령어가 실행되고 echo 파일이 생성되었으므로 취약함

[root@jmnote ~]# (for x in {1..200} ; do echo "for x$x in ; do :"; done; for x in {1..200} ; do echo done ; done) | bash ||
> echo "CVE-2014-7187 vulnerable, word_lineno"
bash: line 129: syntax error near `x129'
bash: line 129: `for x129 in ; do :'
CVE-2014-7187 vulnerable, word_lineno

→ echo ... 명령어가 수행되었으므로 취약함

4 Bash 버전 확인

Bash 버전 확인 문서를 참고하십시오.

[root@jmnote ~]# rpm -qa | grep bash
bash-3.2-32.el5

5 Bash 업데이트

[root@jmnote ~]# yum update bash
... (생략)
===========================================================================================
 Package          Arch               Version                     Repository           Size
===========================================================================================
Updating:
 bash             x86_64             3.2-33.el5_10.4             updates             1.8 M

Transaction Summary
===========================================================================================
Install       0 Package(s)
Upgrade       1 Package(s)

Total download size: 1.8 M
Is this ok [y/N]: y

... (생략)
Updated:
  bash.x86_64 0:3.2-33.el5_10.4                                                            

Complete!

6 확인 2 (안전)

[root@jmnote ~]# env x='() { :;}; echo vulnerable' bash -c "echo this is a test"
this is a test

[root@jmnote ~]# rm -f echo; env X='() { (a)=>\' sh -c "echo date"; cat echo
date
cat: echo: No such file or directory

[root@jmnote ~]# (for x in {1..200} ; do echo "for x$x in ; do :"; done; for x in {1..200} ; do echo done ; done) | bash ||
> echo "CVE-2014-7187 vulnerable, word_lineno"

7 같이 보기

• Bash 버전 확인
• 하트블리드
• 쉘

8 참고 자료

• https://en.wikipedia.org/wiki/Shellshock_(software_bug)
• http://hacksum.net/vuln/cve-2014-6271-gnu-bash-원격코드-인젝션-취약점/
• https://access.redhat.com/ko/node/1215293
• GNU Bash 원격명령 실행 취약점 대응방안 권고《KISA 취약점분석팀》 2014-09-30