Vulnerabilities > CVE-2017-15654 - Use of Insufficiently Random Values vulnerability in Asus Asuswrt 3.0.0.4.378/3.0.0.4.380.7743
Attack vector
NETWORK Attack complexity
HIGH Privileges required
NONE Confidentiality impact
HIGH Integrity impact
HIGH Availability impact
HIGH Summary
Highly predictable session tokens in the HTTPd server in all current versions (<= 3.0.0.4.380.7743) of Asus asuswrt allow gaining administrative router access.
Vulnerable Configurations
| Part | Description | Count |
|---|---|---|
| OS | 3 |
Common Weakness Enumeration (CWE)
Common Attack Pattern Enumeration and Classification (CAPEC)
- Brute Force In this attack, some asset (information, functionality, identity, etc.) is protected by a finite secret value. The attacker attempts to gain access to this asset by using trial-and-error to exhaustively explore all the possible secret values in the hope of finding the secret (or a value that is functionally equivalent) that will unlock the asset. Examples of secrets can include, but are not limited to, passwords, encryption keys, database lookup keys, and initial values to one-way functions. The key factor in this attack is the attackers' ability to explore the possible secret space rapidly. This, in turn, is a function of the size of the secret space and the computational power the attacker is able to bring to bear on the problem. If the attacker has modest resources and the secret space is large, the challenge facing the attacker is intractable. While the defender cannot control the resources available to an attacker, they can control the size of the secret space. Creating a large secret space involves selecting one's secret from as large a field of equally likely alternative secrets as possible and ensuring that an attacker is unable to reduce the size of this field using available clues or cryptanalysis. Doing this is more difficult than it sounds since elimination of patterns (which, in turn, would provide an attacker clues that would help them reduce the space of potential secrets) is difficult to do using deterministic machines, such as computers. Assuming a finite secret space, a brute force attack will eventually succeed. The defender must rely on making sure that the time and resources necessary to do so will exceed the value of the information. For example, a secret space that will likely take hundreds of years to explore is likely safe from raw-brute force attacks.
- Signature Spoofing by Key Recreation An attacker obtains an authoritative or reputable signer's private signature key by exploiting a cryptographic weakness in the signature algorithm or pseudorandom number generation and then uses this key to forge signatures from the original signer to mislead a victim into performing actions that benefit the attacker.
- Session Credential Falsification through Prediction This attack targets predictable session ID in order to gain privileges. The attacker can predict the session ID used during a transaction to perform spoofing and session hijacking.
Seebug
| bulletinFamily | exploit |
| description | ### 1 ASUSWRT <= 3.0.0.4.382.18495 >3.0.0.4.376 - multiple vulnerabilities in httpd server (all versions of AsusWRT at the time of report to vendor, for previous 376 version see next section) #### 1. Highly predictable session tokens The session token is generated for an authenticated user using stdlib rand function. The token generation code looks as follows: ``` ┌──── │ char *generate_token(void){ │ int a=0, b=0, c=0, d=0; │ //char create_token[32]={0}; │ memset(gen_token,0,sizeof(gen_token)); │ srand (time(NULL)); //VULNERABLE │ a=rand(); │ b=rand(); │ c=rand(); │ d=rand(); │ snprintf(gen_token, sizeof(gen_token),"%d%d%d%d", a, b, c, d); │ return gen_token; │ } └──── ``` The code initializes the random number generator each time a token is generated with router epoch time. An attacker can guess a token knowing more or less the time the administrator has logged in. CVE: CVE-2017-15654 Suggested CVSS v3: 8.3 AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H (Attacker needs administrator interaction and a way to overcome administrator IP check - see next point) Timeline: • 17.09.2017 - vendor notified • 07.11.2017 - vendor releases a fixed version 3.0.0.4.382.18495 #### 2. Not sufficient logged user IP validation An attacker who knows the session token can walkaround the IP verification mechanism by sending requests with a special useragent. The following PoC will download current router configuration even if issued from a different than the logged user IP address: ``` curl "http://ROUTERADDRESS/s.CFG"; -H "Cookie: asus_token=TOKEN" -H 'User-Agent: asusrouter-asusrouter-asusrouter-asusrouter' ``` CVE: CVE-2017-15653 Suggested CVSS v3: 8.3 AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H (Attacker needs the session token to execute any action without IP check - see point above) Timeline: • 17.09.2017 - vendor notified • 07.11.2017 - vendor releases a fixed version 3.0.0.4.382.18495 Note to vendor/mitre: for clarity please assign separate CVE to this vulnerability #### 3. Password stored in plain text Asus routers store password in plain text in NVRAM memory. Executing nvram show, or downloading the backup file and decoding it allows anyone to read the administrator password. Having access to telnet (shell) one can execute: ``` nvram show ``` For reading password from backup file see the exploit below. CVE: CVE-2017-15656 Timeline: • 17.09.2017 - vendor notified • 03.01.2018 - vendor stated that the NVRAM will be crypted in February this year #### 4. Logged-in information disclousure An unauthenticated attacker can retrieve information about a logged-in session (if and who [IP address] is currently logged in). This itself is not a vulnerability but together with the two previous it allows for a easy exploit. ``` curl "http://ROUTERADDRESS/Nologin.asp"; ``` Taking all the four together it is easy to gain router access by waiting for an administrator login and retrieving the login/password using his token. Finally it is possible to download the backup file and read the administrator login and password. A ready script is attached to this message. Suggested CVSS v3 for all three (1-3): 9.6 AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H ### 2 ASUSWRT <=3.0.0.4.376.* This vulnerability affects new Asus routers with not up-to-date firmware, as well as some older end-of-life routers (e.g. RT-N65R, RT-N65U) #### 1. Heap buffer overflow in multiple HTTP headers allows for an unauthenticated remote code execution. Multiple buffer overflow vulnerabilities in HTTPd server in Asus asuswrt version <=3.0.0.4.376.X. All have been fixed in version 3.0.0.4.378, but this vulnerability was not previously disclosed. Some end-of-life routers have this version as the newest so are vulnerable at this time. This vulnerability allows for RCE with administrator rights when the administrator visits serveral pages. For example the "Host:" header is vulnerable and allows to override the SystemCmd variable which then allows for RCE when the administrator visits serveral pages (for example the network tools router tab). PoC (after running this script, when the administrator visists one of several pages which trigger commands e.g. the network tools tab, the script is being run and outputs the contents of nvram to a css file which can be retrived without authentication) ``` curl 'http://routerIP:8080' -H "Host: xxxxxxxxxxxxxx $(for i in $(seq 1 9700); do echo -n " "; done) \$(nvram show > /www/user/nvram.css )" ``` CVE: CVE-2017-15655 Suggested CVSS v3: 9.6 AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H (Administrator needs to login and visit certain page at the router website) Timeline: • 17.09.2017 - vendor notified • 18.09.2017 - vendor REFUSED to fix the vulnerability as the routers using the vulnerable firmware are already EOL ALERT: Users having routers not upgradable from 3.0.0.4.376.* or less should CLOSE the http from WAN and should restrict the access to management port from LAN as well! |
| id | SSV:97086 |
| last seen | 2018-01-18 |
| modified | 2018-01-17 |
| published | 2018-01-17 |
| reporter | Root |
| title | Multiple vulnerabilities in all versions of ASUS routers |