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fix null query filter conversion from sigma to query string query (op…
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…ensearch-project#722)

* fix null query filter conversion from sigma to query string query

Signed-off-by: Surya Sashank Nistala <snistala@amazon.com>

* fix rule to query conversion tests for null filter

Signed-off-by: Surya Sashank Nistala <snistala@amazon.com>

* enhance test to verify non null doc doesnt match null query

Signed-off-by: Surya Sashank Nistala <snistala@amazon.com>

---------

Signed-off-by: Surya Sashank Nistala <snistala@amazon.com>
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@eirsep @engechas
eirsep authored and engechas committed Mar 14, 2024
1 parent 7357bb4 commit 1e9d5d8
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Showing 3 changed files with 72 additions and 3 deletions.
2 changes: 1 addition & 1 deletion src/main/java/org/opensearch/securityanalytics/rules/backend/OSQueryBackend.java
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Original file line number Diff line number Diff line change
Expand Up @@ -131,7 +131,7 @@ public OSQueryBackend(String ruleCategory, boolean collectErrors, boolean enable
this.reEscapeChar = "\\";
this.reExpression = "%s: /%s/";
this.cidrExpression = "%s: \"%s\"";
this.fieldNullExpression = "%s: null";
this.fieldNullExpression = "%s: (NOT [* TO *])";
this.unboundValueStrExpression = "\"%s\"";
this.unboundValueNumExpression = "\"%s\"";
this.unboundWildcardExpression = "%s";
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69 changes: 69 additions & 0 deletions src/test/java/org/opensearch/securityanalytics/TestHelpers.java
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Expand Up @@ -168,6 +168,37 @@ public static String randomRule() {
"level: high";
}


public static String randomNullRule() {
return "title: null field\n" +
"id: 5f92fff9-82e2-48eb-8fc1-8b133556a551\n" +
"description: Detects remote RPC calls to possibly abuse remote encryption service via MS-EFSR\n" +
"references:\n" +
" - https://attack.mitre.org/tactics/TA0008/\n" +
" - https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-36942\n" +
" - https://github.com/jsecurity101/MSRPC-to-ATTACK/blob/main/documents/MS-EFSR.md\n" +
" - https://github.com/zeronetworks/rpcfirewall\n" +
" - https://zeronetworks.com/blog/stopping_lateral_movement_via_the_rpc_firewall/\n" +
"tags:\n" +
" - attack.defense_evasion\n" +
"status: experimental\n" +
"author: Sagie Dulce, Dekel Paz\n" +
"date: 2022/01/01\n" +
"modified: 2022/01/01\n" +
"logsource:\n" +
" product: rpc_firewall\n" +
" category: application\n" +
" definition: 'Requirements: install and apply the RPC Firew all to all processes with \"audit:true action:block uuid:df1941c5-fe89-4e79-bf10-463657acf44d or c681d488-d850-11d0-8c52-00c04fd90f7e'\n" +
"detection:\n" +
" selection:\n" +
" EventID: 22\n" +
" RecordNumber: null\n" +
" condition: selection\n" +
"falsepositives:\n" +
" - Legitimate usage of remote file encryption\n" +
"level: high";
}

public static String randomRuleWithKeywords() {
return "title: Remote Encrypting File System Abuse\n" +
"id: 5f92fff9-82e2-48eb-8fc1-8b133556a551\n" +
Expand Down Expand Up @@ -1353,6 +1384,44 @@ public static String randomDocOnlyNumericAndText(int severity, int version, Stri
return String.format(Locale.ROOT, doc, severity, version, opCode);
}

public static String randomDocWithNullField() {
return "{\n" +
"\"@timestamp\":\"2020-02-04T14:59:39.343541+00:00\",\n" +
"\"EventTime\":\"2020-02-04T14:59:39.343541+00:00\",\n" +
"\"HostName\":\"EC2AMAZ-EPO7HKA\",\n" +
"\"Keywords\":\"9223372036854775808\",\n" +
"\"SeverityValue\":2,\n" +
"\"Severity\":\"INFO\",\n" +
"\"EventID\":22,\n" +
"\"SourceName\":\"Microsoft-Windows-Sysmon\",\n" +
"\"ProviderGuid\":\"{5770385F-C22A-43E0-BF4C-06F5698FFBD9}\",\n" +
"\"Version\":5,\n" +
"\"TaskValue\":22,\n" +
"\"OpcodeValue\":0,\n" +
"\"RecordNumber\":null,\n" +
"\"ExecutionProcessID\":1996,\n" +
"\"ExecutionThreadID\":2616,\n" +
"\"Channel\":\"Microsoft-Windows-Sysmon/Operational\",\n" +
"\"Domain\":\"NTAUTHORITY\",\n" +
"\"AccountName\":\"SYSTEM\",\n" +
"\"UserID\":\"S-1-5-18\",\n" +
"\"AccountType\":\"User\",\n" +
"\"Message\":\"Dns query:\\r\\nRuleName: \\r\\nUtcTime: 2020-02-04 14:59:38.349\\r\\nProcessGuid: {b3c285a4-3cda-5dc0-0000-001077270b00}\\r\\nProcessId: 1904\\r\\nQueryName: EC2AMAZ-EPO7HKA\\r\\nQueryStatus: 0\\r\\nQueryResults: 172.31.46.38;\\r\\nImage: C:\\\\Program Files\\\\nxlog\\\\nxlog.exe\",\n" +
"\"Category\":\"Dns query (rule: DnsQuery)\",\n" +
"\"Opcode\":\"Info\",\n" +
"\"UtcTime\":\"2020-02-04 14:59:38.349\",\n" +
"\"ProcessGuid\":\"{b3c285a4-3cda-5dc0-0000-001077270b00}\",\n" +
"\"ProcessId\":\"1904\",\"QueryName\":\"EC2AMAZ-EPO7HKA\",\"QueryStatus\":\"0\",\n" +
"\"QueryResults\":\"172.31.46.38;\",\n" +
"\"Image\":\"C:\\\\Program Files\\\\nxlog\\\\regsvr32.exe\",\n" +
"\"EventReceivedTime\":\"2020-02-04T14:59:40.780905+00:00\",\n" +
"\"SourceModuleName\":\"in\",\n" +
"\"SourceModuleType\":\"im_msvistalog\",\n" +
"\"CommandLine\": \"eachtest\",\n" +
"\"Initiated\": \"true\"\n" +
"}";
}

public static String randomDoc() {
return "{\n" +
"\"EventTime\":\"2020-02-04T14:59:39.343541+00:00\",\n" +
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4 changes: 2 additions & 2 deletions src/test/java/org/opensearch/securityanalytics/rules/backend/QueryBackendTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -282,7 +282,7 @@ public void testConvertValueNull() throws IOException, SigmaError {
" sel:\n" +
" fieldA1: null\n" +
" condition: sel", false));
Assert.assertEquals("mappedA: null", queries.get(0).toString());
Assert.assertEquals("mappedA: (NOT [* TO *])", queries.get(0).toString());
}

public void testConvertValueRegex() throws IOException, SigmaError {
Expand Down Expand Up @@ -525,7 +525,7 @@ public void testConvertOrInUnallowedValueType() throws IOException, SigmaError {
" - value2\n" +
" - null\n" +
" condition: sel", false));
Assert.assertEquals("(mappedA: \"value1\") OR (mappedA: \"value2\") OR (mappedA: null)", queries.get(0).toString());
Assert.assertEquals("(mappedA: \"value1\") OR (mappedA: \"value2\") OR (mappedA: (NOT [* TO *]))", queries.get(0).toString());
}

public void testConvertOrInListNumbers() throws IOException, SigmaError {
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