cbcvebase.
CVE-2022-26937
published 2022-05-10

CVE-2022-26937: Windows Network File System Remote Code Execution Vulnerability

PriorityP277critical9.8CVSS 3.1
AVNACLPRNUINSUCHIHAH
EPSS
76.77%
99.5th percentile
Windows Network File System Remote Code Execution Vulnerability

Affected

21 ranges
VendorProductVersion rangeFixed in
microsoftwindows_server
microsoftwindows_server_2008
microsoftwindows_server_2008
microsoftwindows_server_2008_r2_service_pack_1>= 6.1.7601.0 < 6.1.7601.259546.1.7601.25954
microsoftwindows_server_2008_service_pack_2>= 6.0.6003.0 < 6.0.6003.214816.0.6003.21481
microsoftwindows_server_2012
microsoftwindows_server_2012>= 6.2.9200.0 < 6.2.9200.237146.2.9200.23714
microsoftwindows_server_2012_r2>= 6.3.9600.0 < 6.3.9600.203716.3.9600.20371
microsoftwindows_server_2016>= 10.0.14393.0 < 10.0.14393.512510.0.14393.5125
microsoftwindows_server_2019>= 10.0.17763.0 < 10.0.17763.292810.0.17763.2928
microsoftwindows_server_2022>= 10.0.20348.0 < 10.0.20348.70710.0.20348.707
microsoftwindows_server_version_20h2>= 10.0.0 < 10.0.19042.170610.0.19042.1706
msrcwindows_server_2008_for_32-bit_systems_service_pack_2
msrcwindows_server_2008_for_x64-based_systems_service_pack_2
msrcwindows_server_2008_r2_for_x64-based_systems_service_pack_1
msrcwindows_server_2012
msrcwindows_server_2012_r2
msrcwindows_server_2016
msrcwindows_server_2019
msrcwindows_server_2022
msrcwindows_server_version_20h2

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 utf8string fields with lengths greater than 0x1000, which are suspicious and indicative of an exploitation attempt.
  • Focus detection on NFS4 messages where fields parsed by Nfs4SvrXdrpDecode_STRING (as defined in RFC 3530) contain abnormally large utf8string values, as the vulnerable code path is XdrDecodeString called from Nfs4SvrXdrpDecode_STRING.
  • Look for unauthenticated, specially crafted ONC RPC calls to the NFS service over the network; the exploit requires no authentication.
  • Parse ONC RPC Fragment headers on TCP sessions to NFS; monitor for oversized utf8string buffer requests in NFSv2/NFSv3 NFS4 messages, as the attacker would request a large buffer to increase probability of failed allocation.
  • ·CVE-2022-26937 affects NFSv2 and NFSv3 only; NFSv4.1 is NOT vulnerable. The temporary mitigation is to disable NFSv2 and NFSv3 via PowerShell before patching.
  • ·The string length threshold of 0x1000 for suspicious detection is based on typical file path string limits and may need tuning per server configuration.
  • ·Do NOT use the NFSv4.1 downgrade mitigation for CVE-2023-24941 unless CVE-2022-26937 (May 2022 patch) has already been applied, as NFSv2/v3 are vulnerable to CVE-2022-26937.

CVSS provenance

nvdv3.19.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
nvdv2.07.5HIGHAV:N/AC:L/Au:N/C:P/I:P/A:P
vendor_msrc9.8CRITICAL
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