<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class="">Hi Justin,</div><div class=""><br class=""></div><div class="">You cannot rely on the first IP in XFF (I guess you're doing that at the moment), but you can rely on the next-to-last. The last one is added to XFF by Varnish before entering 'vcl_recv', and the next-to-last is added by the ALB. That's the client IP as seen by the ALB and cannot be forged by clients.</div><div class=""><br class=""></div><div class="">Best,</div><div class=""><br class=""></div><div class="">--</div><div class="">Carlos Abalde<br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 19 Aug 2021, at 22:11, Justin Lloyd <<a href="mailto:justinl@arena.net" class="">justinl@arena.net</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta charset="UTF-8" class=""><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Hi all,<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Is anyone else running Varnish behind AWS ALBs? I just encountered an issue today with how I have been using X-Forwarded-For to check against a Varnish ACL in that is more restrictive than the ALB’s security group, but I realized the hard way that since X-Forwarded-For can be arbitrarily set, a malicious actor can set it to an address that is permitted by the Varnish ACL, whether through guessing or other knowledge. Since Varnish gets XFF from the ALB, which in turn trusts existing XFF headers, you can’t then really trust client.ip since it’s just taken from XFF. Unless I’m missing something...<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">I’ve opened a support case with AWS to see if there’s a way to configure an ALB to not trust XFF and use the IP from the original TCP connection, but I’m not hopeful. I’ll likely have to go back to using two ALBs rather than one relatively open one and one with a Varnish ACL for tigher controls to a certain subset of the web sites behind the single ALB.<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Justin<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div></div><span style="caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">_______________________________________________</span><br style="caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">varnish-misc mailing list</span><br style="caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><a href="mailto:varnish-misc@varnish-cache.org" style="font-family: Menlo-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">varnish-misc@varnish-cache.org</a><br style="caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><a href="https://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc" style="font-family: Menlo-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">https://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc</a></div></blockquote></div><br class=""></div></body></html>