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As reported by Ben Kallus in the following thread: https://www.mail-archive.com/haproxy@formilux.org/msg46471.html there exist some agents which mistakenly accept CRLF inside quoted chunk extensions, making it possible to fool them by injecting one extra chunk they won't see for example, or making them miss the end of the body depending on how it's done. Haproxy, like most other agents nowadays, doesn't care at all about chunk extensions and just drops them, in agreement with the spec. However, as discussed, since chunk extensions are basically never used except for attacks, and that the cost of just matching quote pairs and checking backslashed quotes is escape consistency remains relatively low, it can make sense to add such a check to abort the message parsing when this situation is encountered. Note that it has to be done at two places, because there is a fast path and a slow path for chunk parsing. Also note that it *will* cause transfers using improperly formatted chunk extensions to fail, but since these are really not used, and that the likelihood of them being used but improperly quoted certainly is much lower than the risk of crossing a broken parser on the client's request path or on the server's response path, we consider the risk as acceptable. The test is not subject to the configurable parser exceptions and it's very unlikely that it will ever be needed. Since this is done in 3.4 which will be LTS, this patch will have to be backported to 3.3 so that any unlikely trouble gets a chance to be detected before users upgrade to 3.4. Thanks to Ben for the discussion, and to Rajat Raghav for sparking it in the first place even though the original report was mistaken. Cc: Ben Kallus <benjamin.p.kallus.gr@dartmouth.edu> Cc: Rajat Raghav <xclow3n@gmail.com> Cc: Christopher Faulet <cfaulet@haproxy.com> |
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