RC4 Is Still Considered Harmful
Summary: Google Project Zero researcher James Forshaw found a Windows Kerberos vulnerability (issue 2310) in June 2022 in which RC4 encryption handling allowed authentication as another user if an attacker could interpose on Kerberos traffic to and from the KDC or if the target user had pre-authentication disabled. The post details how RC4-HMAC keys derive from the unsalted, single-pass MD4 hash of a user's password, enabling brute-force attacks via Kerberoasting and AS-REP Roasting, and describes a private encryption type, RSADSI RC4-MD4 (type -128), that uses only the first 8 bytes of a 16-byte key with no blinding.
What you should know: RC4 remains enabled by default in Windows Kerberos, and the key protecting a user is only as strong as their password - a service account with a configured SPN and a weak password can be cracked offline from a single requested ticket. Disabling RC4 network-wide is uncommon for compatibility reasons, leaving the Protected Users Group as the narrower mitigation.
Read the original at Google Project Zero ↗
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- Vulnerabilities & Patching
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