cbcvebase.
CVE-2018-5999
published 2018-01-22

CVE-2018-5999: An issue was discovered in AsusWRT before 3.0.0.4.384_10007. In the handle_request function in router/httpd/httpd.c, processing of POST requests continues even…

PriorityP189critical9.8CVSS 3.0
AVNACLPRNUINSUCHIHAH
ITWEXPLOITVulnCheck KEV
Exploited in the wild
EPSS
87.15%
99.7th percentile
An issue was discovered in AsusWRT before 3.0.0.4.384_10007. In the handle_request function in router/httpd/httpd.c, processing of POST requests continues even if authentication fails.

Affected

1 ranges
VendorProductVersion rangeFixed in
asusasuswrt< 3.0.0.4.384_100073.0.0.4.384_10007

Detection & IOCsextracted from sources · hover to see the quote

url/vpnupload.cgi
portUDP/9999
command/usr/sbin/telnetd -l /bin/sh -p <random_port>
otherateCommand_flag=1 (POST form-data field)
bytes
0x0C 0x15 0x33 0x00 (NET_SERVICE_ID_IBOX_INFO, NET_PACKET_TYPE_CMD, NET_CMD_ID_MANU_CMD) — UDP infosvr PKT_SYSCMD header
  • Detect unauthenticated HTTP POST requests to /vpnupload.cgi on AsusWRT devices; legitimate access requires authentication.
  • Alert on UDP packets to port 9999 (infosvr) containing the byte sequence 0x0C 0x15 0x33 0x00 at the start of the payload, indicating a PKT_SYSCMD (NET_CMD_ID_MANU_CMD) command execution attempt.
  • Monitor for spawning of telnetd processes on AsusWRT routers, especially with the arguments '-l /bin/sh', which indicates post-exploitation shell access.
  • Flag multipart/form-data POST requests to /vpnupload.cgi that include the field 'ateCommand_flag' set to '1', which enables the privileged command mode (PKT_SYSCMD).
  • The authentication bypass occurs in handle_request() in router/httpd/httpd.c — POST request handler->input() is called even when auth_result != 0; look for POST requests to the router HTTP server that lack valid session cookies or Authorization headers.
  • ·The exploit is LAN-scoped only; the attack vector requires the attacker to be on the same local network as the vulnerable AsusWRT router.
  • ·The telnetd backdoor is spawned on a random high port (1024–65535), so port-based blocking alone is insufficient; process-level monitoring for telnetd is needed.
  • ·Confirmed affected version is 3.0.0.4.380.7743; all versions before 3.0.0.4.384.10007 are potentially vulnerable.
  • ·The infosvr UDP packet is fixed at 512 bytes (info_pdu_size = 512); padding bytes are random, so signature matching should focus on the first 4 header bytes rather than the full packet.

CVSS provenance

nvdv3.09.8CRITICALCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
nvdv2.010.0CRITICALAV:N/AC:L/Au:N/C:C/I:C/A:C
vulncheck9.8CRITICAL
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