Apache Update: TLS Certificate Authentication Bypass with HTTP/2 (CVE-2016-4979)
Apache released an important update today to fix a vulnerability that affects servers that have http/2 enabled and use TLS client certificates for authentication.
Apache 2.4.18-20 are vulnerable if:
- TLS certificates are used for authenticating clients (look for the "SSLVerifyClient require" directive in your configuration file)
- http/2 is enabled. (see if the "Protocols" line includes h2 and/or h2c).
Only access over http/2 is affected. Access via http/1.1 is still properly controlled even if http/2 is enabled. Over TLS, clients that suport http/2 will likely use it over http/1.1.
http/2 is not enabled by default in any currently shipping version of Apache.
To quickly check your network traffic for http/2 use, you can use this tshark line:
tshark -Y 'ssl.handshake.extensions_alpn_str == "h2"' -n -i en0 \
-T fields -e ip.src -e ip.dst -e ssl.handshake.type -e ssl.handshake.extensions_server_name \
-e ssl.handshake.extensions_alpn_str
It will list the client requests as well as the server responses that contain http/2 including the host name that the client is trying to reach. For example:
10.5.1.12 216.58.192.66 1 cm.g.doubleclick.net h2,spdy/3.1,http/1.1
216.58.192.66 10.5.1.12 2 h2
In this handshake, the client offers http/2, spdy/3.1 as well as http/1.1 to cm.g.doubleclick.net . The server then selects http/2 (h2).
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Comments
I tried to run your command and get errors.
When trying the tshark command.
tshark -Y 'ssl.handshake.extensions_alpn_str == "h2"' -n -i en0 \
-T fields -e ip.src -e ip.dst -e ssl.handshake.type -e ssl.handshake.extensions_server_name \
-e ssl.handshake.extensions_alpn_str
I get "That string isn't a valid capture filter (Syntax error).
See the User's Guide for a description of the capture filter syntax.
0 packets captured.
Do you know how to fix this? Pretty new to the game yet but love learning.
Also, is there a Snort rule that can be used to find this?
Thanks again. Love the show and love the news update.
Anonymous
Jul 6th 2016
8 years ago
I know the one I had in my Ubuntu 14.04 didn't "ssl.handshake.extensions_alpn_str" part at all, it's only newer versions of tshark that supports that extension.
PS. Ubuntu 16.04 has a working version.
Anonymous
Jul 8th 2016
8 years ago