SB2019100925 - MitM attack in Microsoft Windows NTLM MIC and NTLMv2 implementations

Description

This security bulletin contains information about 2 vulnerabilities.

1) Man-in-the-Middle (MitM) attack (CVE-ID: CVE-2019-1166)

CWE-ID: CWE-300 - Channel Accessible by Non-Endpoint ('Man-in-the-Middle')

CVSSv4: CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green

The vulnerability allows a remote attacker to tamper with the NTLM exchange.

The vulnerability exists due to insufficient integrity check for NTLM packets. A remote attacker can modify flags of the NTLM packet without invalidating the signature and bypass the NTLM MIC (Message Integrity Check) protection.

2) Man-in-the-Middle (MitM) attack (CVE-ID: CVE-2019-1338)

CWE-ID: CWE-300 - Channel Accessible by Non-Endpoint ('Man-in-the-Middle')

CVSSv4: CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green

The vulnerability allows a remote attacker to tamper with the NTLMv2 exchange.

The vulnerability exists due to insufficient integrity check for NTLMv2 packets, when the client is also sending LMv2 responses. A remote attacker with ability to modify NTLM traffic exchange can bypass the NTLMv2 protection and gain the ability to downgrade NTLM security features.

Remediation

Install update from vendor's website.

References

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-1166
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-1338