Phicomm K2 Firmware

The use of the RSA algorithm without OAEP, or any other padding scheme, in telnetd_startup, allows an unauthenticated attacker on the local area network to achieve a significant degree of control over the "plaintext" to which an arbitrary blob of ciphertext will be decrypted by OpenSSL's RSA_public_decrypt() function. This weakness allows the attacker to manipulate the various iterations of the telnetd startup state machine and eventually obtain a root shell on the device, by means of an exchange of crafted UDP packets. In all versions but K2 22.5.9.163 and K3C 32.1.15.93 a successful attack also requires the exploitation of a null-byte interaction error (CVE-2022-25219).

A null byte interaction error has been discovered in the code that the telnetd_startup daemon uses to construct a pair of ephemeral passwords that allow a user to spawn a telnet service on the router, and to ensure that the telnet service persists upon reboot. By means of a crafted exchange of UDP packets, an unauthenticated attacker on the local network can leverage this null byte interaction error in such a way as to make those ephemeral passwords predictable (with 1-in-94 odds). Since the attacker must manipulate data processed by the OpenSSL function RSA_public_decrypt(), successful exploitation of this vulnerability depends on the use of an unpadded RSA cipher (CVE-2022-25218).

Phicomm k2 v22.6.529.216 was discovered to contain a command injection vulnerability via the function luci.sys.call.

Phicomm K2G v22.6.3.20 was discovered to contain a command injection vulnerability via the autoUpTime parameter in the automatic upgrade function.

Phicomm K2 v22.6.534.263 was discovered to contain a command injection vulnerability via the autoUpTime parameter in the automatic upgrade function.

Use of a hard-coded cryptographic key pair by the telnetd_startup service allows an attacker on the local area network to obtain a root shell on the device over telnet. The builds of telnetd_startup included in the version 22.5.9.163 of the K2 firmware, and version 32.1.15.93 of the K3C firmware (possibly amongst many other releases) included both the private and public RSA keys. The remaining versions cited here redacted the private key, but left the public key unchanged. An attacker in possession of the leaked private key may, through a scripted exchange of UDP packets, instruct telnetd_startup to spawn an unauthenticated telnet shell as root, by means of which they can then obtain complete control of the device. A consequence of the limited availablility of firmware images for testing is that models and versions not listed here may share this vulnerability.

Phicomm K2G v22.6.3.20 was discovered to store the root and admin passwords in plaintext.

Phicomm K2 v22.6.534.263 was discovered to store the root and admin passwords in plaintext.

Improper access control on the LocalClientList.asp interface allows an unauthenticated remote attacker to obtain sensitive information concerning devices on the local area network, including IP and MAC addresses. Improper access control on the wirelesssetup.asp interface allows an unauthenticated remote attacker to obtain the WPA passphrases for the 2.4GHz and 5.0GHz wireless networks. This is particularly dangerous given that the K2G setup wizard presents the user with the option of using the same password for the 2.4Ghz network and the administrative interface, by clicking a checkbox. When Remote Managment is enabled, these endpoints are exposed to the WAN.

Improper physical access control and use of hard-coded credentials in /etc/passwd permits an attacker with physical access to obtain a root shell via an unprotected UART port on the device. The same port exposes an unauthenticated Das U-Boot BIOS shell.

Improper access control on the LocalMACConfig.asp interface allows an unauthenticated remote attacker to add (or remove) client MAC addresses to (or from) a list of banned hosts. Clients with those MAC addresses are then prevented from accessing either the WAN or the router itself.