Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: defer destroy_previous_session() until after NTLM authentication
In ntlm_authenticate(), destroy_previous_session() is called using a user pointer resolved from the client-supplied NTLM blob username field before the NTLMv2 response is validated. An authenticated attacker can set the NTLM blob username to match a victim account and set PreviousSessionId to the victim’s session ID; destroy_previous_session() destroys the victim’s session while ksmbd_decode_ntlmssp_auth_blob() subsequently rejects the request with -EPERM.
Move destroy_previous_session() and the prev_id assignment to after ksmbd_decode_ntlmssp_auth_blob() returns success and use sess->user rather than the pre-authentication lookup result. This matches the ordering already used by krb5_authenticate(), where destroy_previous_session() is called only after ksmbd_krb5_authenticate() returns success.
Details
- Affected product:
- Debian 10 ELS
- Affected packages:
- linux @ 4.19.0