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common-vulnerabilities.md

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Common vulnerabilities

Shellshock

  • Also known as bashdoor or bash bug
  • Privilege escalation vulnerability enabling arbitrary commands execution
  • 📝 Caused by family of security bugs in the Unix Bash shell
  • Related CVE entries include: • CVE-2014-6271, CVE-2014-6277 • CVE-2014-6278, CVE-2014-7169 • CVE-2014-7186, CVE-2014-7187
  • Achieved by manipulating the environment variable list and then cause Bash to run
  • Upon startup Bash parser executes scripts saved as environment variables
  • E.g. $ env x='() { :;}; echo vulnerable' bash -c "echo this is a test"
    • Prints first vulnerable then this is a test
  • To exploit there needs to be away to talk to Bash.
  • Often exploits websites using CGI
    • CGI stands for "Common Gateway Interface"
    • In Apache it's done using mod_cgi
      • Way to let Apache execute script files and send the output to the client
      • Apache passes information to CGI scripts using environment variables
    • E.g. if you you have a HTTP header named Sike in your request, you will have an environment variable named HTTP_SIKE available in your CGI.
  • Big impact

Detecting Shellshock using Nmap

  • Can use Shellshock script with Nmap scripting engine.
  • nmap -sV -p 80 --script http-shellshock --script-args uri=/cgi-bin/blabla.sh,cmd=ls 192.168.122.17.8
    • -sV: detect services and versions
    • -p: port 80, you can also do -p- to scan for entire port range
    • --script: You can test different scripts / vulnerabilities, choose anything from scripts page
    • --script-args: optional, 2 args, uri and cmd

SSL/TLS Vulnerabilities

Heartbleed

  • 📝 Bug in OpenSSL library a widely used implementation of TLS.
  • Introduced and patched in April 2014.
  • Results from improper input validation (no boundary check) in TLS heartbeat extension
  • Causing server to send more data in the memory than it allowed
    • Classified as buffer over-read
  • Flow
    • TLS/DTLS Heartbeat flow:
      • Client: Send me 4 letter word: "bird" -> Server: "bird"
    • Malicious Heartbeat flow:
      • Client: Send me 500 letter word: "bird" -> Server: bird. Server master key is 3131531535. User Carol wants to change password to "password 1 2 3"...
  • Reverse Heartbleed
    • Malicious server exploiting Heartbleed to read from client memory.
  • Millions of webpages were affected, still there are IoT devices are vulnerable (see shodan search)
  • Had big impact, some known ones are stealing of millions of patient records, hijacking accounts CEO impersonation ....

    • "Heartbleed is the worst vulnerability found" - Forbes

  • Can be exploited
    • Using Nmap: nmap -p 443 --script ssl-heartbleed <target>
      • Will return "State: NOT VULNERABLE" if not vulnerable.
    • Using Metasploit: openssl_heartbleed module

POODLE

  • POODLE stands for "Padding Oracle On Downgraded Legacy Encryption"
  • 📝 Forcing a degradation to a vulnerable SSL/TLS version
    • TLS handshakes are walked down the connection until a usable/vulnerable one is found
    • Exploits backwards compatibility
  • Man-in-the-middle exploit
  • Affects both SSL and TLS
    • Vulnerability was disclosed in October 2014 for SSL.
    • A variation used to attack TLS was disclosed in December 2014.
  • POODLE attack against SSL
    • Takes advantage of Internet and security software clients' fallback to SSL 3.0.
    • Attackers make 256 SSL 3.0 request on average to reveal a single byte.
  • POODLE attack against TLS
    • Caused by some implementation not following the TLS specifications.
    • Exploits CBC encryption mode in the TLS 1.0 - 1.2 protocols

FREAK

  • Stands for "Factoring RSA Export Keys"
  • Man-in-the-middle attack forcing downgrade of RSA key to a weaker length
  • Enables successful brute-force attacks.
  • Exploits cryptographic weakness in the SSL/TLS protocols

SSL/TLS Renegotiation

  • 📝 Leads to plaintext injection attacks against SSL 3.0 and all current versions of TLS
  • Background
    • Marsh Ray and Steve Dispensa release a document discussing a vulnerability in the design of TLS – November 4, 2009
    • Turkish grad student, Anil Kurmus, exploits the vulnerability to steal Twitter login credentials – November 10, 2009
  • Mitigation
    • Quick fix was the renegotiation
    • Proposed standard (RFC 5746) is to verify previous renegotiation handshakes between client and server.
  • Testing
    • Use open_ssl s_client -connect <website>:443
    • Then type R for renegotiate and [ENTER]

DROWN

  • Stands for "Decrypting RSA with Obsolete and Weakened eNcryption"
  • Exploits modern SSL/TLS suites by exploiting their obsolete SSLv2 protocol support.
  • The only viable countermeasure is to disable SSLv2 on all servers