Caching

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Caching
Panther's real-time analysis engine examines events one-by-one and sometimes it's helpful to keep state across invocations. To accommodate stateful checks, rules can cache values by using built-in helper functions.
Importing the Helpers
The first step is to import the open source helper library:
import panther_oss_helpers
You may import specific functions:
from panther_oss_helpers import increment_counter
Counters
To implement a counter-based rule, use one or more of the following functions:
get_counter: Get the latest counter value
increment_counter: Add to the counter (default of 1)
reset_counter: Reset the counter to 0
set_key_expiration: Set the lifetime of the counter
The rule below provides a demonstration of using counters.
from panther_oss_helpers import increment_counter, set_key_expiration, reset_counter
​
​
def rule(event):
    # Filter to only analyze AccessDenied calls
    if event.get('errorCode') != 'AccessDenied':
        return False
​
    # Create our counter key, which should be fairly unique
    key = '{}-AccessDeniedCounter'.format(event['userIdentity'].get('arn'))
​
    # Increment the counter, and then check the current value
    hourly_error_count = increment_counter(key)
    if hourly_error_count == 1:
        set_key_expiration(time.time() + 3600)
    elif failure_hourly_count >= 10:
    # If it exceeds our threshold, reset and then return an alert
        reset_counter(key)
        return True
    return False
The key-value pairs are temporarily stored in apanther-kv-store DynamoDB table.
String Sets
To keep track of sets of strings, use the following functions:
get_string_set: Get the string set's current value
put_string_set: Overwrite a string set
add_to_string_set: Add one or more strings to a set
remove_from_string_set: Remove one or more strings from a set
reset_string_set: Empty the set
from panther_oss_helpers import add_to_string_set
​
​
def rule(event):
    if event['eventName'] != 'AssumeRole':
        return False
​
    role_arn = event['requestParameters'].get('roleArn')
    if not role_arn:
        return False
​
    role_arn_key = '{}-UniqueSourceIPs'.format(role_arn)
    ip_addr = event['sourceIPAddress']
​
    previously_seen_ips = get_string_set(role_arn_key)
​
    # If this the only value, trust on first use
    if len(previously_seen_ips) == 0:
        add_to_string_set(role_arn_key, ip_addr)
        return False
​
    if ip_addr not in previously_seen_ips:
        return True
​
    return False
Detection Packs
Data Models
Last modified 1mo ago
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Outline
Importing the Helpers
Counters
String Sets