Description of problem:
When sssd is configured to use Kerberos for authentication
(auth_provider = krb5 in a domain section) any password is accepted as
valid under the following conditions:
- the system is offline, i.e. the KDC configured with the option
krb5_kdcip cannot be reached
- the user who tries to authenticate has a valid TGT for the Kerberos
realm configured with to option krb5_realm in his credential cache
Short term fix:
- disable Kerberos authentication and use alternatives if possible
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Configure an SSSD system to authenticate against a Kerberos KDC
2. Log in as a user while SSSD is online.
3. Verify that the user has a valid TGT for the Kerberos realm.
4. Unplug the network cable.
5. Lock the display.
6. The user will be able to unlock the display with any password.
Additionally, this can make a system network-vulnerable, as if the SSSD is in the offline state (either the KDC or the identity server is unreachable), an attacker can log into any account that has a valid TGT.
Passwords are not properly verified against the cached credentials. Any password will be treated as a valid authentication.
Authentication should succeed with only the valid credentials.
The only current workaround for this problem is to disable Kerberos authentication on affected machines until a patched binary is available.
Fedora is being tracked via bug 553233
Fixed now in upstream release 1.0.1:
sssd-1.0.1-1.fc11 has been pushed to the Fedora 11 stable repository. If problems still persist, please make note of it in this bug report.
sssd-1.0.1-1.fc12 has been pushed to the Fedora 12 stable repository. If problems still persist, please make note of it in this bug report.