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Sapphire tickets ​

Theory ​

Sapphire tickets are similar to Diamond tickets in the way the ticket is not forged, but instead based on a legitimate one obtained after a request. The difference lays in how the PAC is modified. The Diamond ticket approach modifies the legitimate PAC. In the Sapphire ticket approach, the PAC of another powerful user is obtained through an S4U2self+u2u trick. This PAC then replaces the one featured in the legitimate ticket. The resulting ticket is an assembly of legitimate elements, and follows a standard ticket request, which makes it then most difficult silver/golden ticket variant to detect.

Practice ​

Since Diamond tickets modify PACs on-the-fly to include arbitrary group IDs, chances are some detection software are (of will be) able to detect discrepancies between a PAC's values and actual AD relationships (e.g. a PAC indicates a user belongs to some groups when in fact it doesn't).

Sapphire tickets are an alternative to obtaining similar tickets in a stealthier way, by including a legitimate powerful user's PAC in the ticket. There will be no discrepancy anymore between what's in the PAC and what's in Active Directory.

The powerful user's PAC can be obtained through an S4U2self+u2u trick.

From UNIX-like systems, Impacket's ticketer (Python) script can be used for such purposes with the -impersonate argument.

Nota bene: the -user-id argument will be used to build the "Requestor" PAC structure, which could be needed in up-to-date environments (see warning at the bottom of this page).

The arguments used to customize the PAC will be ignored (-groups, -extra-sid,-duration), the required domain SID (-domain-sid) as well as the username supplied in the positional argument (baduser in this case). All these information will be kept as-is from the PAC obtained beforehand using the "S4U2self + U2U" technique.

bash
ticketer.py -request -impersonate 'domainadmin' \
-domain 'DOMAIN.FQDN' -user 'domain_user' -password 'password' \
-nthash 'krbtgt NT hash' -aesKey 'krbtgt AES key' \
-user-id '1115' -domain-sid 'S-1-5-21-...' \
'baduser'

In 2021, Microsoft issued a patch (KB5008380) for CVE-2021-42287 (see samaccountname-spoofing.md). The patch is explained a bit more in this blogpost. When the patch entered its enforcement phase (Oct. 11th 2022), it made the Sapphire Ticket attack harder to conduct.

The patch introduced two new structures inside a TGT's PAC: "Requestor" (PAC_REQUESTOR) and "Attributes" (PAC_ATTRIBUTES_INFO). Those structures are now required in TGTs for all up-to-date environments after the patch enforcement phase, and a KDC_ERR_TGT_REVOKED error is raised if a TGT is used without them.

Necessary updates were brought to offensive tooling like Impacket (PR# 1391 and 1545) and Rubeus (PR# 105).

However, since the Sapphire Ticket technique relies on a S4U2self + U2U service ticket request to obtain a privileged user's PAC, the PAC doesn't feature the two new "Requestor" and "Attributes" structures. This is probably because the two new structures are only included in TGT's PACs and not service tickets PACs.

When using the Sapphire Ticket technique to forge a TGT, if the two structures are missing from the forget ticket, a KDC_ERR_TGT_REVOKED error will be raised in environments that have the patch installed.

Resources ​

https://unit42.paloaltonetworks.com/next-gen-kerberos-attacks/