GuardDuty S3 finding types

The following findings are specific to Amazon S3 resources and will have a Resource Type of S3Bucket if the data source is CloudTrail data events for S3, or AccessKey if the data source is CloudTrail management events. The severity and details of the findings will differ based on the finding type and the permission associated with the bucket.

The findings listed here include the data sources and models used to generate that finding type. For more information data sources and models, see Foundational data sources.

Important

Findings with a data source of CloudTrail data events for S3 are only generated if you have S3 protection enabled for GuardDuty. S3 protection is enabled by default in all accounts created after July 31, 2020. For information about how to enable or disable S3 protection, see Amazon S3 Protection in Amazon GuardDuty

For all S3Bucket type findings, it is recommended that you examine the permissions on the bucket in question and the permissions of any users involved in the finding, if the activity is unexpected see the remediation recommendations detailed in Remediating a compromised S3 bucket.

Discovery:S3/AnomalousBehavior

An API commonly used to discover S3 objects was invoked in an anomalous way.

Default severity: Low

• Data source: CloudTrail data events for S3

This finding informs you that an IAM entity has invoked an S3 API to discover S3 buckets in your environment, such as ListObjects. This type of activity is associated with the discovery stage of an attack wherein an attacker gathers information to determine if your AWS environment is susceptible to a broader attack. This activity is suspicious because the IAM entity invoked the API in an unusual way. For example, an IAM entity with no previous history invokes an S3 API, or an IAM entity invokes an S3 API from an unusual location.

This API was identified as anomalous by GuardDuty's anomaly detection machine learning (ML) model. The ML model evaluates all the API requests in your account and identifies anomalous events that are associated with techniques used by adversaries. It tracks various factors of the API requests, such as the user who made the request, the location from which the request was made, the specific API that was requested, the bucket that was requested, and the number of API calls made. For more information on which factors of the API request are unusual for the user identity that invoked the request, see Finding details.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

Discovery:S3/MaliciousIPCaller

An S3 API commonly used to discover resources in an AWS environment was invoked from a known malicious IP address.

Default severity: High

• Data source: CloudTrail data events for S3

This finding informs you that an S3 API operation was invoked from an IP address that is associated with known malicious activity. The observed API is commonly associated with the discovery stage of an attack when an adversary is gathering information about your AWS environment. Examples include GetObjectAcl and ListObjects.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

Discovery:S3/MaliciousIPCaller.Custom

An S3 API was invoked from an IP address on a custom threat list.

Default severity: High

• Data source: CloudTrail data events for S3

This finding informs you that an S3 API, such as GetObjectAcl or ListObjects, was invoked from an IP address that is included on a threat list that you uploaded. The threat list associated with this finding is listed in the Additional information section of a finding's details. This type of activity is associated with the discovery stage of an attack wherein an attacker is gathering information to determine if your AWS environment is susceptible to a broader attack.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

Discovery:S3/TorIPCaller

An S3 API was invoked from a Tor exit node IP address.

Default severity: Medium

• Data source: CloudTrail data events for S3

This finding informs you that an S3 API, such as GetObjectAcl or ListObjects, was invoked from a Tor exit node IP address. This type of activity is associated with the discovery stage of an attack wherein an attacker is gathering information to determine if your AWS environment is susceptible to a broader attack. Tor is software for enabling anonymous communication. It encrypts and randomly bounces communications through relays between a series of network nodes. The last Tor node is called the exit node. This can indicate unauthorized access to your AWS resources with the intent of hiding the attacker's true identity.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

Exfiltration:S3/AnomalousBehavior

An IAM entity invoked an S3 API in a suspicious way.

Default severity: High

• Data source: CloudTrail data events for S3

This finding informs you that an IAM entity is making API calls that involve an S3 bucket and this activity differs from that entity's established baseline. The API call used in this activity is associated with the exfiltration stage of an attack, wherein an attacker attempts to collect data. This activity is suspicious because the IAM entity invoked the API in an unusual way. For example, an IAM entity with no previous history invokes an S3 API, or an IAM entity invokes an S3 API from an unusual location.

This API was identified as anomalous by GuardDuty's anomaly detection machine learning (ML) model. The ML model evaluates all the API requests in your account and identifies anomalous events that are associated with techniques used by adversaries. It tracks various factors of the API requests, such as the user who made the request, the location from which the request was made, the specific API that was requested, the bucket that was requested, and the number of API calls made. For more information on which factors of the API request are unusual for the user identity that invoked the request, see Finding details.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

Exfiltration:S3/MaliciousIPCaller

An S3 API commonly used to collect data from an AWS environment was invoked from a known malicious IP address.

Default severity: High

• Data source: CloudTrail data events for S3

This finding informs you that an S3 API operation was invoked from an IP address that is associated with known malicious activity. The observed API is commonly associated with exfiltration tactics where an adversary is trying to collect data from your network. Examples include GetObject and CopyObject.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

Impact:S3/AnomalousBehavior.Delete

An IAM entity invoked an S3 API that attempts to delete data in a suspicious way.

Default severity: High

• Data source: CloudTrail data events for S3

This finding informs you that an IAM entity in your AWS environment is making API calls that involve an S3 bucket, and this behavior differs from that entity's established baseline. The API call used in this activity is associated with an attack that attempts to delete data. This activity is suspicious because the IAM entity invoked the API in an unusual way. For example, an IAM entity with no previous history invokes an S3 API, or an IAM entity invokes an S3 API from an unusual location.

This API was identified as anomalous by GuardDuty's anomaly detection machine learning (ML) model. The ML model evaluates all the API requests in your account and identifies anomalous events that are associated with techniques used by adversaries. It tracks various factors of the API requests, such as the user who made the request, the location from which the request was made, the specific API that was requested, the bucket that was requested, and the number of API calls made. For more information on which factors of the API request are unusual for the user identity that invoked the request, see Finding details.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

We recommend an audit of your S3 bucket's contents to determine if you the previous object version can or should be restored.

Impact:S3/AnomalousBehavior.Permission

An API commonly used to set the access control list (ACL) permissions was invoked in an anomalous way.

Default severity: High

• Data source: CloudTrail data events for S3

This finding informs you that an IAM entity in your AWS environment has changed a bucket policy or ACL on the listed S3 buckets. This change may publicly expose your S3 buckets to all the authenticated AWS users.

This API was identified as anomalous by GuardDuty's anomaly detection machine learning (ML) model. The ML model evaluates all the API requests in your account and identifies anomalous events that are associated with techniques used by adversaries. It tracks various factors of the API requests, such as the user who made the request, the location from which the request was made, the specific API that was requested, the bucket that was requested, and the number of API calls made. For more information on which factors of the API request are unusual for the user identity that invoked the request, see Finding details.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

We recommend an audit of your S3 bucket's contents to ensure that no objects were unexpectedly allowed to be accessed publicly.

Impact:S3/AnomalousBehavior.Write

An IAM entity invoked an S3 API that attempts to write data in a suspicious way.

Default severity: Medium

• Data source: CloudTrail data events for S3

This finding informs you that an IAM entity in your AWS environment is making API calls that involve an S3 bucket, and this behavior differs from that entity's established baseline. The API call used in this activity is associated with an attack that attempts to write data. This activity is suspicious because the IAM entity invoked the API in an unusual way. For example, an IAM entity with no previous history invokes an S3 API, or an IAM entity invokes an S3 API from an unusual location.

This API was identified as anomalous by GuardDuty's anomaly detection machine learning (ML) model. The ML model evaluates all the API requests in your account and identifies anomalous events that are associated with techniques used by adversaries. It tracks various factors of the API requests, such as the user who made the request, the location from which the request was made, the specific API that was requested, the bucket that was requested, and the number of API calls made. For more information on which factors of the API request are unusual for the user identity that invoked the request, see Finding details.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

We recommend an audit of your S3 bucket's contents to ensure that this API call didn't write malicious or unauthorized data.

Impact:S3/MaliciousIPCaller

An S3 API commonly used to tamper with data or processes in an AWS environment was invoked from a known malicious IP address.

Default severity: High

• Data source: CloudTrail data events for S3

This finding informs you that an S3 API operation was invoked from an IP address that is associated with known malicious activity. The observed API is commonly associated with impact tactics where an adversary is trying manipulate, interrupt, or destroy data within your AWS environment. Examples include PutObject and PutObjectAcl.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

PenTest:S3/KaliLinux

An S3 API was invoked from a Kali Linux machine.

Default severity: Medium

• Data source: CloudTrail data events for S3

This finding informs you that a machine running Kali Linux is making S3 API calls using credentials that belong to your AWS account. Your credentials might be compromised. Kali Linux is a popular penetration testing tool that security professionals use to identify weaknesses in EC2 instances that require patching. Attackers also use this tool to find EC2 configuration weaknesses and gain unauthorized access to your AWS environment.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

PenTest:S3/ParrotLinux

An S3 API was invoked from a Parrot Security Linux machine.

Default severity: Medium

• Data source: CloudTrail data events for S3

This finding informs you that a machine running Parrot Security Linux is making S3 API calls using credentials that belong to your AWS account. Your credentials might be compromised. Parrot Security Linux is a popular penetration testing tool that security professionals use to identify weaknesses in EC2 instances that require patching. Attackers also use this tool to find EC2 configuration weaknesses and gain unauthorized access to your AWS environment.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

PenTest:S3/PentooLinux

An S3 API was invoked from a Pentoo Linux machine.

Default severity: Medium

• Data source: CloudTrail data events for S3

This finding informs you that a machine running Pentoo Linux is making S3 API calls using credentials that belong to your AWS account. Your credentials might be compromised. Pentoo Linux is a popular penetration testing tool that security professionals use to identify weaknesses in EC2 instances that require patching. Attackers also use this tool to find EC2 configuration weaknesses and gain unauthorized access to your AWS environment.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

Policy:S3/AccountBlockPublicAccessDisabled

An IAM entity invoked an API used to disable S3 Block Public Access on an account.

Default severity: Low

• Data source: CloudTrail management events

This finding informs you that Amazon S3 Block Public Access was disabled at the account level. When S3 Block Public Access settings are enabled, they are used to filter the policies or access control lists (ACLs) on buckets as a security measure to prevent inadvertent public exposure of data.

Typically, S3 Block Public Access is turned off in an account to allow public access to a bucket or to the objects in the bucket. When S3 Block Public Access is disabled for an account, access to your buckets is controlled by the policies, ACLs, or bucket-level Block Public Access settings applied to your individual buckets. This does not necessarily mean that the buckets are shared publicly, but that you should audit the permissions applied to the buckets to confirm that they provide the appropriate level of access.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

Policy:S3/BucketAnonymousAccessGranted

An IAM principal has granted access to an S3 bucket to the internet by changing bucket policies or ACLs.

Default severity: High

• Data source: CloudTrail management events

This finding informs you that the listed S3 bucket has been made publicly accessible on the internet because an IAM entity has changed a bucket policy or ACL on that bucket. After a policy or ACL change is detected, uses automated reasoning powered by Zelkova, to determine if the bucket is publicly accessible.

Note

If a bucket's ACLs or bucket policies are configured to explicitly deny or to deny all, this finding may not reflect the current state of the bucket. This finding will not reflect any S3 Block Public Access settings that may have been enabled for your S3 bucket. In such cases, the effectivePermission value in the finding will be marked as UNKNOWN.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

Policy:S3/BucketBlockPublicAccessDisabled

An IAM entity invoked an API used to disable S3 Block Public Access on a bucket.

Default severity: Low

• Data source: CloudTrail management events

This finding informs you that Block Public Access was disabled for the listed S3 bucket. When enabled, S3 Block Public Access settings are used to filter the policies or access control lists (ACLs) applied to buckets as a security measure to prevent inadvertent public exposure of data.

Typically, S3 Block Public Access is turned off on a bucket to allow public access to the bucket or to the objects within. When S3 Block Public Access is disabled for a bucket, access to the bucket is controlled by the policies or ACLs applied to it. This does not mean that the bucket is shared publicly, but you should audit the policies and ACLs applied to the bucket to confirm that appropriate permissions are applied.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

Policy:S3/BucketPublicAccessGranted

An IAM principal has granted public access to an S3 bucket to all AWS users by changing bucket policies or ACLs.

Default severity: High

• Data source: CloudTrail management events

This finding informs you that the listed S3 bucket has been publicly exposed to all authenticated AWS users because an IAM entity has changed a bucket policy or ACL on that S3 bucket. After a policy or ACL change is detected, uses automated reasoning powered by Zelkova, to determine if the bucket is publicly accessible.

Note

If a bucket's ACLs or bucket policies are configured to explicitly deny or to deny all, this finding may not reflect the current state of the bucket. This finding will not reflect any S3 Block Public Access settings that may have been enabled for your S3 bucket. In such cases, the effectivePermission value in the finding will be marked as UNKNOWN.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

Stealth:S3/ServerAccessLoggingDisabled

S3 server access logging was disabled for a bucket.

Default severity: Low

• Data source: CloudTrail management events

This finding informs you that S3 server access logging is disabled for a bucket within your AWS environment. If disabled, no web request logs are created for any attempts to access the identified S3 bucket, however, S3 management API calls to the bucket, such as DeleteBucket, are still tracked. If S3 data event logging is enabled through CloudTrail for this bucket, web requests for objects within the bucket will still be tracked. Disabling logging is a technique used by unauthorized users in order to evade detection. To learn more about S3 logs, see S3 Server Access Logging and S3 Logging Options .

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

UnauthorizedAccess:S3/MaliciousIPCaller.Custom

An S3 API was invoked from an IP address on a custom threat list.

Default severity: High

• Data source: CloudTrail data events for S3

This finding informs you that an S3 API operation, for example, PutObject or PutObjectAcl, was invoked from an IP address that is included on a threat list that you uploaded. The threat list associated with this finding is listed in the Additional information section of a finding's details.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.

UnauthorizedAccess:S3/TorIPCaller

An S3 API was invoked from a Tor exit node IP address.

Default severity: High

• Data source: CloudTrail data events for S3

This finding informs you that an S3 API operation, such as PutObject or PutObjectAcl, was invoked from a Tor exit node IP address. Tor is software for enabling anonymous communication. It encrypts and randomly bounces communications through relays between a series of network nodes. The last Tor node is called the exit node. This finding can indicate unauthorized access to your AWS resources with the intent of hiding the attacker's true identity.

Remediation recommendations:

If this activity is unexpected for the associated principal, it may indicate that the credentials have been exposed or your S3 permissions are not restrictive enough. For more information, see Remediating a compromised S3 bucket.