Event 4649: A replay attack was detected.

Adversaries may exploit software vulnerabilities in an attempt to collect credentials. Exploitation of a software vulnerability occurs when an adversary takes advantage of a programming error in a program, service, or within the operating system software or kernel itself to execute adversary-controlled code.  Credentialing and authentication mechanisms may be targeted for exploitation by adversaries as a means to gain access to useful credentials or circumvent the process to gain authenticated access to systems. One example of this is `MS14-068`, which targets Kerberos and can be used to forge Kerberos tickets using domain user permissions.(Citation: Technet MS14-068)(Citation: ADSecurity Detecting Forged Tickets) Another example of this is replay attacks, in which the adversary intercepts data packets sent between parties and then later replays these packets. If services don't properly validate authentication requests, these replayed packets may allow an adversary to impersonate one of the parties and gain unauthorized access or privileges.(Citation: Bugcrowd Replay Attack)(Citation: Comparitech Replay Attack)(Citation: Microsoft Midnight Blizzard Replay Attack) Such exploitation has been demonstrated in cloud environments as well. For example, adversaries have exploited vulnerabilities in public cloud infrastructure that allowed for unintended authentication token creation and renewal.(Citation: Storm-0558 techniques for unauthorized email access) Exploitation for credential access may also result in Privilege Escalation depending on the process targeted or credentials obtained.

Adversaries may “pass the ticket” using stolen Kerberos tickets to move laterally within an environment, bypassing normal system access controls. Pass the ticket (PtT) is a method of authenticating to a system using Kerberos tickets without having access to an account's password. Kerberos authentication can be used as the first step to lateral movement to a remote system. When preforming PtT, valid Kerberos tickets for [Valid Accounts](https://attack.mitre.org/techniques/T1078) are captured by [OS Credential Dumping](https://attack.mitre.org/techniques/T1003). A user's service tickets or ticket granting ticket (TGT) may be obtained, depending on the level of access. A service ticket allows for access to a particular resource, whereas a TGT can be used to request service tickets from the Ticket Granting Service (TGS) to access any resource the user has privileges to access.(Citation: ADSecurity AD Kerberos Attacks)(Citation: GentilKiwi Pass the Ticket) A [Silver Ticket](https://attack.mitre.org/techniques/T1558/002) can be obtained for services that use Kerberos as an authentication mechanism and are used to generate tickets to access that particular resource and the system that hosts the resource (e.g., SharePoint).(Citation: ADSecurity AD Kerberos Attacks) A [Golden Ticket](https://attack.mitre.org/techniques/T1558/001) can be obtained for the domain using the Key Distribution Service account KRBTGT account NTLM hash, which enables generation of TGTs for any account in Active Directory.(Citation: Campbell 2014) Adversaries may also create a valid Kerberos ticket using other user information, such as stolen password hashes or AES keys. For example, "overpassing the hash" involves using a NTLM password hash to authenticate as a user (i.e. [Pass the Hash](https://attack.mitre.org/techniques/T1550/002)) while also using the password hash to create a valid Kerberos ticket.(Citation: Stealthbits Overpass-the-Hash)

Adversaries may attempt to subvert Kerberos authentication by stealing or forging Kerberos tickets to enable [Pass the Ticket](https://attack.mitre.org/techniques/T1550/003). Kerberos is an authentication protocol widely used in modern Windows domain environments. In Kerberos environments, referred to as “realms”, there are three basic participants: client, service, and Key Distribution Center (KDC).(Citation: ADSecurity Kerberos Ring Decoder) Clients request access to a service and through the exchange of Kerberos tickets, originating from KDC, they are granted access after having successfully authenticated. The KDC is responsible for both authentication and ticket granting. Adversaries may attempt to abuse Kerberos by stealing tickets or forging tickets to enable unauthorized access. On Windows, the built-in <code>klist</code> utility can be used to list and analyze cached Kerberos tickets.(Citation: Microsoft Klist)