TP-LINK Cloud Cameras NCXXX Remote NULL Pointer Dereference

2020.04.02
Credit: Pietro Oliva
Risk: Low
Local: No
Remote: Yes
CWE: CWE-476

Vulnerability title: TP-LINK Cloud Cameras NCXXX Remote NULL Pointer Dereference Author: Pietro Oliva CVE: CVE-2020-10231 Vendor: TP-LINK Product: NC200, NC210, NC220, NC230, NC250, NC260, NC450 Affected version: NC200 <= 2.1.8 build 171109, NC210 <= 1.0.9 build 171214, NC220 <= 1.3.0 build 180105, NC230 <= 1.3.0 build 171205, NC250 <= 1.3.0 build 171205, NC260 <= 1.5.1 build 190805, NC450 <= 1.5.0 build 181022 Description: The issue is located in the httpLoginRpm method of the ipcamera binary (handler method for /login.fcgi), where after successful login, there is no check for NULL in the return value of httpGetEnv(environment, "HTTP_USER_AGENT"). Shortly after that, there is a call to strstr(user_agent_string, "Firefox") and if a User-Agent header is not specified by the client, httpGetEnv will return NULL, and a NULL pointer dereference occurs when calling strstr, with consequent crash of the ipcamera process. Impact: After the crash, the web interface on port 80 will not be available anymore. Exploitation: An attacker could exploit this issue by just sending a login request with valid credentials (such as admin or limited user), but without an user-agent HTTP header. Default credentials can be used to bypass the credentials requirement. Evidence: The disassembly of affected code from an NC200 camera is shown below: 0x0047dca0 lw a0, (user_arg) 0x0047dca4 lw a1, (password_arg) 0x0047dca8 lw t9, -sym.swUMMatchPassword(gp) 0x0047dcac nop 0x0047dcb0 jalr t9 0x0047dcb4 nop 0x0047dcb8 lw gp, (saved_gp) 0x0047dcbc sw v0, (auth_result) 0x0047dcc0 lw v0, (auth_result) 0x0047dcc4 nop 0x0047dcc8 bnez v0, 0x47de34 0x0047dccc nop 0x0047dcd0 sw zero, (arg_54h) 0x0047dcd4 lw a0, (environment) 0x0047dcd8 lw a1, -0x7fe4(gp) 0x0047dcdc nop 0x0047dce0 addiu a1, a1, -0x7cb0 ; "HTTP_USER_AGENT" 0x0047dce4 lw t9, -sym.httpGetEnv(gp) 0x0047dce8 nop 0x0047dcec jalr t9 0x0047dcf0 nop 0x0047dcf4 lw gp, (saved_gp) 0x0047dcf8 sw v0, (user_agent_ptr) 0x0047dcfc lw a0, (user_agent_ptr) ; <== This pointer could be NULL 0x0047dd00 lw a1, -0x7fe4(gp) 0x0047dd04 nop 0x0047dd08 addiu a1, a1, -0x7ca0 ; "Firefox" 0x0047dd0c lw t9, -sym.imp.strstr(gp) 0x0047dd10 nop 0x0047dd14 jalr t9 Disclosure timeline: 2nd December 2019 - Initial vulnerability report for NC200. 4th December 2019 - Vendor confirms vulnerablity but does not start fixing due to the product being end-of-life. 4th December 2019 - Notified vendor the vulnerability details will be public and it should be fixed. 6th December 2019 - Thanks for your opinion, we will discuss and write back to you. <silence> 7th February 2020 - Notified vendor issue exists on NC450 and possibly all models in between. Fixed a disclosure deadline in 30 days. 8th February 2020 - Vendor: We will check but please be patient. 18th February 2020 - We failed to reproduce the issue with the provided PoC. <trying to troubleshoot> 24th February 2020 - Reverse engineered all the firmware images on behalf of the vendor and notified they were all vulnerable. 2nd March 2020 - Vendor asks to check fixes for NC200. 2nd March 2020 - Confirmed fix. Asked the vendor to do the same on all cameras. 3rd March 2020 - Vendor will check on other cameras, but will take some time. 3rd March 2020 - Asked the vendor to be quick. 9th March 2020 - Notified CVE identifier to vendor, gave extra week to patch. 9th March 2020 - Vendor is testing fix on all models. 13th March 2020 - Vendor asks to confirm fixes. 13th March 2020 - Confirmed fixes and asked the vendor to publish updates. Disclosure delayed one week to give some time to patch if the vendor published firmware updates. 29th March 2020 - No updates have been made public by the vendor. Releasing details to the public after almost 4 months from initial notification.


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