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https://issues.apache.org/jira/browse/TS-2954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14082223#comment-14082223
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Susan Hinrichs commented on TS-2954:
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Spent yesterday tracing through code. Finally see how this could happen. Need
to reproduce it in my environment to verify. Not clear how much time I'll have
to work on it today, but should have an updated patch available by Monday
morning.
> cache poisoning due to proxy.config.http.use_client_target_addr = 1
> -------------------------------------------------------------------
>
> Key: TS-2954
> URL: https://issues.apache.org/jira/browse/TS-2954
> Project: Traffic Server
> Issue Type: Bug
> Components: Cache, DNS, Security, TProxy
> Reporter: Nikolai Gorchilov
> Assignee: Susan Hinrichs
> Priority: Critical
> Fix For: 5.1.0
>
> Attachments: ts-2954.patch
>
>
> Current implementation of proxy.config.http.use_client_target_addr opens a
> very simple attack vector for cache poisoning in transparent forwarding mode.
> An attacker (or malware installed on innocent end-user computer) puts a fake
> IP for popular website like www.google.com or www.facebook.com in hosts file
> on PC behind the proxy. Once an infected PC requests the webpage in question,
> a cacheable fake response poisons the cache.
> In order to prevent such scenarios (as well as [some
> others|http://www.kb.cert.org/vuls/id/435052]) Squid have implemented a
> mechanism known as [Host Header Forgery
> Detection|http://wiki.squid-cache.org/KnowledgeBase/HostHeaderForgery].
> In short, while requesting an URL from origin server IP as hinted by the
> client, proxy makes independent DNS query in parallel in order to determine
> if client supplied IP belongs to requested domain name. In case of
> discrepancy between DNS and client IP, the transaction shall be flagged as
> non-cacheable to avoid possible cache poisoning, while still serving the
> origin response to the client.
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