cbcvebase.
CVE-2023-24941
published 2023-05-09

CVE-2023-24941: Windows Network File System Remote Code Execution Vulnerability

PriorityP279critical9.8CVSS 3.1
AVNACLPRNUINSUCHIHAH
EPSS
94.68%
99.8th percentile
Windows Network File System Remote Code Execution Vulnerability

Affected

11 ranges
VendorProductVersion rangeFixed in
microsoftwindows_server_2012
microsoftwindows_server_2012>= 6.2.9200.0 < 6.2.9200.242666.2.9200.24266
microsoftwindows_server_2012_r2>= 6.3.9600.0 < 6.3.9600.209696.3.9600.20969
microsoftwindows_server_2016>= 10.0.14393.0 < 10.0.14393.592110.0.14393.5921
microsoftwindows_server_2019>= 10.0.17763.0 < 10.0.17763.437710.0.17763.4377
microsoftwindows_server_2022>= 10.0.20348.0 < 10.0.20348.172610.0.20348.1726
msrcwindows_server_2012
msrcwindows_server_2012_r2
msrcwindows_server_2016
msrcwindows_server_2019
msrcwindows_server_2022

Detection & IOCsextracted from sources · hover to see the quote

port2049/TCP
port2049/UDP
filenamenfssvr.sys
  • Monitor NFS4 traffic on ports 2049/TCP and 2049/UDP for NFSv4.1 calls containing utf8string fields with lengths greater than 0x1000, which are suspicious and indicative of an exploitation attempt.
  • Focus detection on fields parsed by Nfs4SvrXdrpDecode_STRING in all NFS4 messages, as the vulnerable code path XdrDecodeString can only be triggered when called from Nfs4SvrXdrpDecode_STRING.
  • The exploit is unauthenticated and delivered over the network via a specially crafted NFS RPC call; no credentials or user interaction are required, so any unauthenticated NFSv4.1 request with anomalously large utf8string fields should be flagged.
  • When parsing ONC RPC messages over TCP, inspect the Fragment header length field and the utf8string length prefix in NFS4 messages; large declared string lengths (>0x1000) with no legitimate operational justification are attack indicators.
  • ·The vulnerability only affects NFSv4.1; NFSv2.0 and NFSv3.0 are not exploitable by this CVE. Disabling NFSv4.1 is a temporary mitigation, but must NOT be applied unless CVE-2022-26937 (May 2022 patch) is already installed, as that patch addresses critical flaws in NFSv2.0 and NFSv3.0.
  • ·The 0x1000 string-length detection threshold is based on typical file path string limits and may need tuning for environments with non-standard NFS server configurations.

CVSS provenance

nvdv3.19.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
vendor_msrc9.8CRITICAL
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