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Snuffy is a simple command line tool to inspect SSL/TLS connections. It currently supports OpenSSL and NSS.

For background info see the blog post


In order to use snuffy you need to install the headers for the running kernel and LLVM 10.

To install them on ubuntu run:

sudo apt-get -y install build-essential zlib1g-dev \
        llvm-10-dev libclang-10-dev linux-headers-$(uname -r)

On fedora run:

yum install clang llvm llvm-devel zlib-devel kernel-devel
export LLVM_SYS_100_PREFIX=/usr

Finally install snuffy itself running:

cargo install --git snuffy

NOTE: if you installed rust in your home directory, the binary will be placed in $HOME/.cargo/bin/snuffy. If you use sudo to run snuffy, you'll have to use the full path.


Snuffy uses the bpf() syscall, so you need to run it as root or a user with CAP_SYS_ADMIN privileges.

With programs that link to OpenSSL or NSS dynamically

To instruments commands that link to OpenSSL or NSS dynamically, run:

# snuffy --hex-dump --command [COMMAND]

For example to instrument curl:

# snuffy --hex-dump --command /usr/bin/curl # then in another terminal run: curl --http1.1
[6:05:19] Connected to
[6:05:19] Resolved to
[6:05:19] Connected to (
[6:05:19] Write 78 bytes to (
[6:05:19] |47455420 2f204854 54502f31 2e310d0a| GET / HTTP/1.1.. 00000000
[6:05:19] |486f7374 3a207777 772e676f 6f676c65| Host: 00000010
[6:05:19] |2e636f6d 0d0a5573 65722d41 67656e74| .com..User-Agent 00000020
[6:05:19] |3a206375 726c2f37 2e36352e 330d0a41| : curl/7.65.3..A 00000030
[6:05:19] |63636570 743a202a 2f2a0d0a 0d0a|     ccept: */*....   00000040
[6:05:19]                                                        0000004e
[6:05:19] Read 1396 bytes from (
[6:05:19] |48545450 2f312e31 20323030 204f4b0d| HTTP/1.1 200 OK. 00000000
[6:05:19] |0a446174 653a2046 72692c20 30342053| .Date: Fri, 04 S 00000010
[6:05:19] |65702032 30323020 30363a32 303a3033| ep 2020 06:20:03 00000020
[6:05:19] |20474d54 0d0a4578 70697265 733a202d|  GMT..Expires: - 00000030
[6:05:19] |310d0a43 61636865 2d436f6e 74726f6c| 1..Cache-Control 00000040
[6:05:19] |3a207072 69766174 652c206d 61782d61| : private, max-a 00000050

If you omit the --command option, snuffy will intercept all the programs that use OpenSSL or NSS.

NOTE: Firefox links to NSS dynamically, but ships its own and To instrument firefox, you have to provide a config file pointing to those libraries, eg:


With programs that link to OpenSSL or NSS statically

If you want to instrument a program that links statically to OpenSSL or NSS and the symbols have been stripped, you need to provide a configuration file containing the .text section offsets of the TLS functions.

For example for OpenSSL put this in config.toml:

SSL_set_fd = 0xBADDCAFE
SSL_write = 0xDECAFBAD

And for NSS:


(The offsets above are just examples, you need to provide working ones.)

Then run:

# snuffy --hex-dump --command COMMAND --config config.toml

For example assuming zoom-config.toml contains valid OpenSSL offsets for the zoom client:

# snuffy --hex-dump --command /opt/zoom/zoom --config zoom-config.toml # then start zoom
[4:56:18] Connected to
[4:56:18] Resolved to
[4:56:18] Connected to (
[4:56:19] Write 571 bytes to (
[4:56:19] |504f5354 202f7265 6c656173 656e6f74| POST /releasenot 00000000
[4:56:19] |65732048 5454502f 312e310d 0a486f73| es HTTP/1.1..Hos 00000010
[4:56:19] |743a2075 73303477 65622e7a 6f6f6d2e| t: us04web.zoom. 00000020
[4:56:19] |75730d0a 55736572 2d416765 6e743a20| us..User-Agent:  00000030
[4:56:19] |4d6f7a69 6c6c612f 352e3020 285a4f4f| Mozilla/5.0 (ZOO 00000040
[4:56:19] |4d2e4c69 6e757820 5562756e 74752031| M.Linux Ubuntu 1 00000050

[4:56:19] Read 3088 bytes from (
[4:56:19] |48545450 2f312e31 20323030 200d0a44| HTTP/1.1 200 ..D 00000000
[4:56:19] |6174653a 20467269 2c203034 20536570| ate: Fri, 04 Sep 00000010
[4:56:19] |20323032 30203035 3a31313a 30352047|  2020 05:11:05 G 00000020
[4:56:19] |4d540d0a 436f6e74 656e742d 54797065| MT..Content-Type 00000030
[4:56:19] |3a206170 706c6963 6174696f 6e2f782d| : application/x- 00000040
[4:56:19] |70726f74 6f627566 3b636861 72736574| protobuf;charset 00000050