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False Positive 920300 - "Request Missing an Accept Header" #1006

abramz opened this issue Feb 2, 2018 · 2 comments


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@abramz abramz commented Feb 2, 2018

I am using the OWASP 3.0 ruleset that Azure Application Gateways use.
I made this request from my browser and the user agent provided is valid as far as I know.
The request has a valid accept field as well.

macOS 10.13.3
chrome 63.0.3239.132
POST /api/graphql HTTP/1.1
Connection: keep-alive
Content-Length: 1004
Pragma: no-cache
Cache-Control: no-cache
Accept: application/json
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.132 Safari/537.36
Content-Type: application/json
DNT: 1
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
HTTP/1.1 403 ModSecurity Action
Content-Type: text/html
Server: Microsoft-IIS/10.0
Date: Fri, 02 Feb 2018 21:56:08 GMT
Content-Length: 1233

This is what I get from the application gateway logs:

	"operationName": "ApplicationGatewayFirewall",
	"time": "2018-02-02T21:30:01Z",
	"category": "ApplicationGatewayFirewallLog",
	"properties": {
		"instanceId": "ApplicationGatewayRole_IN_2",
		"clientIp": "",
		"clientPort": "0",
		"requestUri": "/",
		"ruleSetType": "OWASP",
		"ruleSetVersion": "3.0",
		"ruleId": "920300",
		"message": "Request Missing an Accept Header",
		"action": "Blocked",
		"site": "Global",
		"details": {
			"message": "Warning. Match of \"pm AppleWebKit Android\" against \"REQUEST_HEADERS:User-Agent\" required.",
			"data": "",
			"file": "rules/REQUEST-920-PROTOCOL-ENFORCEMENT.conf",
			"line": "1247"
		"hostname": ""
@abramz abramz changed the title False Positive 920300 - Request Missing an Accept Header False Positive 920300 - "Request Missing an Accept Header" Feb 2, 2018

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@spartantri spartantri commented Feb 6, 2018

That's strange, rule 920300 in 3.0 check first that the Accept header is not present and also that you user-agent does not contain AppleWebKit, and your example should not match any of those conditions, can you confirm the example request matches the log event?


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@abramz abramz commented Feb 7, 2018

@spartantri I went back through the rules we are hitting and I could not repro this one.

@abramz abramz closed this Feb 7, 2018
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