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varnishcache
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c27afc39
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c27afc39
authored
Oct 06, 2022
by
Martin Blix Grydeland
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VSV00010.rst landing page
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.. _VSV00010:
VSV00010 Varnish Request Smuggling Vulnerability
================================================
Date: <TBD>
A request smuggling attack can be performed on Varnish Cache servers by
requesting that certain headers are made hop-by-hop, preventing the
Varnish Cache servers from forwarding critical headers to the
backend. Among the headers that can be filtered this way are both
`Content-Length` and `Host`, making it possible for an attacker to both
break the HTTP/1 protocol framing, and bypass request to host routing
in VCL.
Versions affected
-----------------
* Varnish Cache releases 7.0.0, 7.0.1, 7.0.2, 7.0.3, 7.1.0, 7.1.1, 7.2.0
Versions not affected
---------------------
* Varnish Cache 7.1.2 (released <TBD>)
* Varnish Cache 7.2.1 (released <TBD>)
* All versions of Varnish Cache 6.0 LTS series and Varnish Cache Plus by
Varnish Software.
* GitHub Varnish Cache master branch at commit <TBD>
Mitigation
----------
If upgrading Varnish is not possible, it is possible to mitigate the
problem by adding the following snippet at the beginning of the `vcl_recv`
VCL function::
sub vcl_recv {
# Start of mitigation for VSV00010
# Tip: Expand the regular expression token list to allow
# additional tokens, e.g. "(close|keep-alive|te|my-header)"
if (regsuball(req.http.connection,
"(?i)((close|keep-alive|te)[ ,]*)", "") !~ "^[ ,]*$") {
return (synth(400));
}
}
This VCL statement would ensure that any attempt to add anything but the
very frequently used tokens `close`, `keep-alive` and `TE` in an incoming
`Connection`-header would be answered with a 400 "Bad request" synthetic
response.
Note that some sites may need to allow other header names as tokens in the
`Connection`-header to function properly. If that is the case for your
site, add any additional headers needed like the commented tip suggests.
Credits
-------
This problem was reported by an external security researcher.
<TODO: Figure out if the OP wants to be credited.>
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