NETRESEC Network Security Blog - Tag : find

Detect TCP content injection attacks with findject

findject logo

NSA's QUANTUM INSERT attack is probably the most well-known TCP packet injection attack due to the Snowden revelations regarding how GCHQ used this method to hack into Belgacom. However, the “Five Eyes” are not the only ones who perform this type of attack on the Internet. We now release a tool to help incident responders to find these types of packet injection attacks.

Photo by Jasper Bongertz at SharkFest EU 2016

I had the opportunity to attend and present at SharkFest Europe last week. My presentation, titled “Dissecting Man-on-the-Side Attacks”, showed how TCP packet injection attacks can be analyzed if they have been recorded in a packet capture. In my talk I used a python script called “”, which reads PCAP files to find TCP packets with duplicate sequence numbers but different content. This script has previously only been shared with vetted parties, but as of my SharkFest presentation findject is now freely available for everyone.

Findject is not the first tool made available to detect TCP content injection attacks. Other detection methods include Suricata's reassembly_overlap_different_data alert, Fox-IT's Bro policy to check for inconsistencies in the first packet with payload, David Stainton's HoneyBadger and Martin Bruse's qisniff. Even though these are all great solutions we found that some of them didn't detect all TCP content injection attacks while others gave too many false positives. We also wanted to have a tool that was fast, portable and simple to use. This led us to create our own TCP injection detection tool.

python /nsm/pcap/live/*
opening /nsm/pcap/live/ppp0.150922_192034.pcap - no injections
opening /nsm/pcap/live/ppp0.150923_081337.pcap
'HTTP/1.1 403 Forbidden\r\nServer: Beaver\r\nCache-Control: no-cache\r\nContent-Type: text/html\r\nContent-Length: 594\r\nConnection: close\r\n\r\n<html>\n<head>\n<meta http-equiv="Content-Type" content="textml;charset=UTF-8" />\n <style>body{background-color:#FFFFFF}</style> \n<title>TestPage</title>\n <script language="javascript" type="text/javascript">\n window.onload = function () { \n document.getElementById("mainFrame").src= ""; \n }\n</script> \n</head>\n <body>\n <iframe style="width:860px; height:500px;position:absolute;margin-left:-430px;margin-top:-250px;top:50%;left:50%;" id="mainFrame" src="" frameborder="0" scrolling="no"></iframe>\n </body>\n </html>\n\n'
'HTTP/1.1 200 OK\r\nContent-Type: text/html\r\nContent-Length: 87\r\nConnection: close\r\n\r\n<html><head><meta http-equiv="refresh" content="0; url=\'\'"></head></html>'

opening /nsm/pcap/live/ppp0.150923_115034.pcap - no injections
opening /nsm/pcap/live/ppp0.150924_071617.pcap - no injections

In the example execution above we can see that detected an injected TCP packet in the file ppp0.150923_081337.pcap, while the other analyzed files contained no injections. The application layer data of the two conflicting TCP segments are printed to standard output with a header indicating whether the segment was the FIRST or LAST one. To find out which segment is the real one and which was the injected one we need to open the PCAP file in either Wireshark, tshark or CapLoader.

tshark -r /nsm/pcap/live/ppp0.150923_083317.pcap -Y "ip.src eq and tcp.port eq 59320" -T fields -e frame.number -e ip.src -e ip.dst -e tcp.seq -e tcp.len -e -e ip.ttl -o "tcp.relative_sequence_numbers: false"
14 402877219 0   0x00002e36 94
25 402877220 726 0x00000d05 70
27 402877220 726 0x00000d05 69
28 402877220 170 0x00002e3e 94

The tshark execution above reveals that three packets sent from the web server's IP ( are carrying data and have the same sequence number (402877220). Packet 25 and 27 are actually identical, while packet 28 is smaller (170 bytes) and has a different payload. The first displayed frame in the tshark output above is the SYN+ACK packet from the TCP 3-way handshake.

So how can we determine which of packets 25, 27 and 28 are real verses injected? Look at the IP-ID and IP-TTL values! Frame 28 has IP-ID and TTL values in line with what we see in the TCP 3-way handshake (TTL=94, IP-ID=0x00002e3e), which implies that this packet is probably authentic. Frames 25 and 27 on the other hand deviate from what we would expect from the server, which tells us that these packets were likely injected (spoofed) into the TCP session through a “man-on-the-side” attack.

findject logo

To learn more about and download the tool, please visit:

Example captures containing TCP content injection attacks can be found on our Publicly Available PCAP Files page under the “Packet Injection Attacks / Man-on-the-Side Attacks” section.

You can also read our blog posts Covert Man-on-the-Side Attacks and Packet Injection Attacks in the Wild to learn more about TCP packet injection attacks.

Posted by Erik Hjelmvik on Tuesday, 25 October 2016 08:45:00 (UTC/GMT)

Tags: #Netresec #PCAP #packet injection #find #python #SharkFest

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Keyword Search in PCAP files

Sherlock Holmes and Magnifying Glass via Inside Croydon A new function in the free version of CapLoader 1.2 is the "Find Keyword" feature. This keyword search functionality makes it possible to seek large capture files for a string or byte pattern super fast!

You might say, so what? PCAP string search can already be done with tools like tcpflow, ngrep and even Wireshark; what's the benefit of adding yet another tool to this list? One benefit is that CapLoader doesn't just give you the packet or content that matched the keyword, it will instead extract the whole TCP or UDP flow that contained the match. CapLoader also supports many different encodings, which is demonstrated in this blog post.

Here are a few quick wins with CapLoader's keyword search feature:

  • Track User-Agent - Search for a specific user agent string to extract all the HTTP traffic from a particular browser or malware.
  • Track Domain Name - Search for a particular domain name to get all DNS lookups as well as web traffic relating to that domain (including HTTP "referer" field matches).
  • Extract Messages - Search for a keyword in e-mail or chat traffic to get the whole e-mail or conversation, not just the single packet that matched.
  • Extract Files - Search for a unique string or byte sequence in a file (such as a piece of malware) to enable extraction of the complete file transfer.

EXAMPLE: DigitalCorpora M57

As an example, let's search the digital corpora file net-2009-12-06-11:59.pcap (149 MB) for the keyword "immortal". Follow these steps in order to veify our analysis using the free edition of CapLoader.

  1. Start CapLoader and select File -> Open URL, enter:
  2. Edit -> Find Keyword (or Ctrl+F), enter "immortal" CapLoader Find Keyword Form
  3. Click the "Find and Select All Matching Flows" button
  4. One TCP flow is now selected (Flow_ID 5469, -> CapLoader with one selected flow
  5. Right click the selected flow (ID 5469) and select "Flow Transcript"
CapLoader Flow Transcript of SMTP email attachment

CapLoader transcript of SMTP email flow

Looks as if an email has been sent with an attachment named "microscope1.jpg". However, the string "immortal" cannot be seen anywhere in the transcript view. The match that CapLoader found was actually in the contents of the attachment, which has been base64 encoded in the SMTP transfer in accordance with RFC 2045 (MIME).

The email attachment can easily be extracted from the PCAP file using NetworkMiner. However, to keep things transparent, let's just do a simple manual verification of the matched data. The first three lines of the email attachment are:

Decoding this with base64 gives us:
0000000: ffd8 ffe0 0010 4a46 4946 0001 0101 0090 ......JFIF......
0000010: 0090 0000 ffdb 0043 0001 0101 0101 0101 .......C........
0000020: 0101 0101 0101 0101 0101 0101 0101 0101 ................
0000030: 0101 0101 0101 0101 0101 0101 0101 0101 ................
0000040: 0101 0101 0101 0101 0101 0101 0101 0101 ................
0000050: 0101 0101 0101 0101 01ff db00 4301 0101 ............C...
0000060: 0101 0101 0101 0101 0101 0101 0101 0101 ................
0000070: 0101 0101 0101 0101 0101 0101 0101 0101 ................
0000080: 7061 7373 776f 7264 3d69 6d6d 6f72 7461 password=immorta
0000090: 6c01 0101 0101 0101 0101 0101 0101 ffc0 l...............

Tools like ngrep, tcpflow and Wireshark won't find any match for the string "immortal" since they don't support searching in base64 encoded data. CapLoader, on the other hand, supports lots of encodings.

Supported Text Encodings

CapLoader currently supports fast searching of text strings in any of the following encodings:

  • Base64 (used in email attachments and HTTP POST's)
  • DNS label encoding (RFC 1035)
  • HTML
  • Quoted Printable (used in body of email messages)
  • Unicode
  • URL encoding
  • UTF8

CapLoader also supports several local character sets, including the following code pages:

  • 437 MS-DOS Latin US
  • 850 MS-DOS Latin 1
  • 932 Japanese
  • 936 Simplified Chinese
  • 949 Korean
  • 1251 Windows Cyrillic (Slavic)
  • 1256 Windows Arabic

Having all these encodings also makes it possible to search network traffic for words like хакер, القراصنة, ハッカー, 黑客 or 해커.

The Art of War by Sun Tzu

Getting CapLoader

CapLoader is a commercial tool that also comes in a free trial edition. The search feature is available in both versions, so feel free to download CapLoader and try it your self!

CapLoader is available from the following URL:

Posted by Erik Hjelmvik on Wednesday, 02 April 2014 13:15:00 (UTC/GMT)

Tags: #search #find #keyword #flow #stream #PCAP #SMTP #transcript #free #network

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Find PCAP files with Google

Perlan, Reykjavik, Iceland by Vestman

We at Netresec maintain a list showing where pcap files can be found on the Internet. Some pcap repositories in this list, like Pcapr and have quite extensive lists of pcap files with indexed meta data about what protocols each pcap file contains.

However, sometimes I find my self in need of traffic from some particular application or protocol, which I'm not able to generate myself. These are situations when I turn to Google for answers. In the spirit of “Google hacking” you can use keywords like “filetype:pcap” or “ext:pcap” to find pcap files. You can also add the letter í (notice the acute accent) to the search query in order to remove some non-pcap files from the search results. The reason why this works is because Google interpret a part of the PCAP file header fields as the letter í. It is also usually a good idea to further limit your search by adding some data specific for the traffic you're looking for into the search query.

You can, for example, use this query to find SMTP traffic (VXNlcm5hbWU6 is 'Username:' Base64 encoded):

í VXNlcm5hbWU6 ext:pcap

You can find Gmail traffic with (notice the use of the gmailchat cookie):

í gmailchat ext:cap

SMB / CIFS traffic can be found with:

í SMB ext:pcap

I think you get the hang of this now...

Happy Googling!

Posted by Erik Hjelmvik on Sunday, 17 July 2011 09:31:00 (UTC/GMT)

Tags: #PCAP #Google

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Recommended Books

» The Practice of Network Security Monitoring, Richard Bejtlich (2013)

» Applied Network Security Monitoring, Chris Sanders and Jason Smith (2013)

» Network Forensics, Sherri Davidoff and Jonathan Ham (2012)

» The Tao of Network Security Monitoring, Richard Bejtlich (2004)

» Practical Packet Analysis, Chris Sanders (2017)

» Windows Forensic Analysis, Harlan Carvey (2009)

» TCP/IP Illustrated, Volume 1, Kevin Fall and Richard Stevens (2011)

» Industrial Network Security, Eric D. Knapp and Joel Langill (2014)