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Seth Manesse and Paul Plasil reported that the "path" sample fetch
function incorrectly accepts '#' as part of the path component. This
can in some cases lead to misrouted requests for rules that would apply
on the suffix:
use_backend static if { path_end .png .jpg .gif .css .js }
Note that this behavior can be selectively configured using
"normalize-uri fragment-encode" and "normalize-uri fragment-strip".
The problem is that while the RFC says that this '#' must never be
emitted, as often it doesn't suggest how servers should handle it. A
diminishing number of servers still do accept it and trim it silently,
while others are rejecting it, as indicated in the conversation below
with other implementers:
https://lists.w3.org/Archives/Public/ietf-http-wg/2023JulSep/0070.html
Looking at logs from publicly exposed servers, such requests appear at
a rate of roughly 1 per million and only come from attacks or poorly
written web crawlers incorrectly following links found on various pages.
Thus it looks like the best solution to this problem is to simply reject
such ambiguous requests by default, and include this in the list of
controls that can be disabled using "option accept-invalid-http-request".
We're already rejecting URIs containing any control char anyway, so we
should also reject '#'.
In the H1 parser for the H1_MSG_RQURI state, there is an accelerated
parser for bytes 0x21..0x7e that has been tightened to 0x24..0x7e (it
should not impact perf since 0x21..0x23 are not supposed to appear in
a URI anyway). This way '#' falls through the fine-grained filter and
we can add the special case for it also conditionned by a check on the
proxy's option "accept-invalid-http-request", with no overhead for the
vast majority of valid URIs. Here this information is available through
h1m->err_pos that's set to -2 when the option is here (so we don't need
to change the API to expose the proxy). Example with a trivial GET
through netcat:
[08/Aug/2023:16:16:52.651] frontend layer1 (#2): invalid request
backend <NONE> (#-1), server <NONE> (#-1), event #0, src 127.0.0.1:50812
buffer starts at 0 (including 0 out), 16361 free,
len 23, wraps at 16336, error at position 7
H1 connection flags 0x00000000, H1 stream flags 0x00000810
H1 msg state MSG_RQURI(4), H1 msg flags 0x00001400
H1 chunk len 0 bytes, H1 body len 0 bytes :
00000 GET /aa#bb HTTP/1.0\r\n
00021 \r\n
This should be progressively backported to all stable versions along with
the following patch:
REGTESTS: http-rules: add accept-invalid-http-request for normalize-uri tests
Similar fixes for h2 and h3 will come in followup patches.
Thanks to Seth Manesse and Paul Plasil for reporting this problem with
detailed explanations.
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The HAProxy documentation has been split into a number of different files for ease of use. Please refer to the following files depending on what you're looking for : - INSTALL for instructions on how to build and install HAProxy - BRANCHES to understand the project's life cycle and what version to use - LICENSE for the project's license - CONTRIBUTING for the process to follow to submit contributions The more detailed documentation is located into the doc/ directory : - doc/intro.txt for a quick introduction on HAProxy - doc/configuration.txt for the configuration's reference manual - doc/lua.txt for the Lua's reference manual - doc/SPOE.txt for how to use the SPOE engine - doc/network-namespaces.txt for how to use network namespaces under Linux - doc/management.txt for the management guide - doc/regression-testing.txt for how to use the regression testing suite - doc/peers.txt for the peers protocol reference - doc/coding-style.txt for how to adopt HAProxy's coding style - doc/internals for developer-specific documentation (not all up to date)