Re: [Asrg] misconception in SPF
Christian Grunfeld <christian.grunfeld@gmail.com> Thu, 06 December 2012 20:15 UTC
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Date: Thu, 06 Dec 2012 17:15:01 -0300
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From: Christian Grunfeld <christian.grunfeld@gmail.com>
To: Anti-Spam Research Group - IRTF <asrg@irtf.org>
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Subject: Re: [Asrg] misconception in SPF
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here is the proof of concept ! an email sent to John Levine claiming to be from ygii-john@www.johnlevine.com !!! Could you please John paste the Received-SPF checks of your mailserver ? Connected to mail1.iecc.com. Escape character is '^]'. 220 mail1.iecc.com mailfront ESMTP EHLO www.johnlevine.com 250-mail1.iecc.com 250-SIZE 0 250-8BITMIME 250-ENHANCEDSTATUSCODES 250 PIPELINING MAIL FROM: ygii-john@www.johnlevine.com 250 2.1.0 Sender accepted. RCPT TO: johnl@taugh.com 250 2.1.5 Recipient accepted. DATA 354 End your message with a period on a line by itself. From: ygii-john@www.johnlevine.com To: johnl@taugh.com Subject: p o c Hi John, just a proof of concept . 250 2.6.0 Accepted message qp 34000 bytes 540 quit 221 2.0.0 Good bye. Connection closed by foreign host. 2012/12/6 Christian Grunfeld <christian.grunfeld@gmail.com>: > Hi, > > Something I found about SPF. I don't know if it is new to you but it > is worth of explanation ! > > As in all the tutorials of SPF, one stays relaxed when lists hosts/ips > that are authorized to send for the domain and then finally closes > with -all. This is true only for that domain but if there are hosts or > subdomains with A records, they must enforce SPF policies ! (this is > not explicit in RFC or at least confusing). > > A single host or subdomain that don't do it can lead to a sender spoofing attack > and pose as someone from our domain without the SPF to detect it. > > This is because when we receive mail from foo@bar.mydomain the SPF > protocol seeks TXT records corresponding to bar.mydomain instead of > TXT record for mydomain. If there is an A record for bar.mydomain but > no TXT "v=spf1 -all" for it, SPF returns "none" although SPF exists > for mydomain ! > > Thus an attacker can inject an email from everywhere claiming that is > from someone@bar.mydomain ! > > As the default policy of SPF should not be "fail if not present" the > solution is to enforce with the records TXT "v = spf1-all" for each A > record that should not send emails! > This also can be made by means of wildcards but it is discourage in the RFC. > > Cheers
- Re: [Asrg] misconception in SPF John Levine
- [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF Derek Diget
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF Paul Smith
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF Andrew Sullivan
- Re: [Asrg] misconception in SPF Paul Smith
- Re: [Asrg] misconception in SPF darxus
- Re: [Asrg] misconception in SPF SM
- Re: [Asrg] misconception in SPF darxus
- Re: [Asrg] misconception in SPF Daniel Feenberg
- Re: [Asrg] misconception in SPF Paul Smith
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] various anti-spam techniques, was misc… John Levine
- Re: [Asrg] various anti-spam techniques, was misc… Rich Kulawiec
- Re: [Asrg] misconception in SPF SM
- Re: [Asrg] misconception in SPF Bill Cole
- Re: [Asrg] various anti-spam techniques, was misc… Christian Grunfeld
- Re: [Asrg] various anti-spam techniques, was misc… John Levine
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF Alessandro Vesely
- Re: [Asrg] misconception in SPF Bill Cole
- Re: [Asrg] misconception in SPF Paul Smith
- Re: [Asrg] misconception in SPF Andrew Sullivan
- Re: [Asrg] misconception in SPF SM
- Re: [Asrg] misconception in SPF Dave Crocker
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF Dave Crocker
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF Seth
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF Franck Martin
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] misconception in SPF Paul Smith
- Re: [Asrg] misconception in SPF Alessandro Vesely
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] misconception in SPF Dotzero
- Re: [Asrg] misconception in SPF Rich Kulawiec
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] misconception in SPF Dave Crocker
- Re: [Asrg] misconception in SPF Chris Lewis
- [Asrg] whitelisting links (was Re: misconception … Dave Crocker
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] misconception in SPF Dave Crocker
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] whitelisting links (was Re: misconcept… Paul Smith
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] whitelisting links (was Re: misconcept… Martijn Grooten
- Re: [Asrg] whitelisting links (was Re: misconcept… darxus
- Re: [Asrg] misconception in SPF Eggert, Lars
- Re: [Asrg] misconception in SPF Christian Grunfeld
- Re: [Asrg] whitelisting links (was Re: misconcept… Dave Crocker
- Re: [Asrg] whitelisting links (was Re: misconcept… Martijn Grooten
- Re: [Asrg] whitelisting links (was Re: misconcept… Michael Thomas
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF Chris Lewis
- Re: [Asrg] whitelisting links (was Re: misconcept… Paul Smith
- Re: [Asrg] whitelisting links (was Re: misconcept… Steve Atkins
- Re: [Asrg] whitelisting links (was Re: misconcept… Martijn Grooten
- Re: [Asrg] whitelisting links (was Re: misconcept… Dave Crocker
- Re: [Asrg] whitelisting links (was Re: misconcept… Martijn Grooten
- Re: [Asrg] whitelisting links (was Re: misconcept… Christian Grunfeld
- Re: [Asrg] whitelisting links (was Re: misconcept… Dave Crocker
- Re: [Asrg] whitelisting links (was Re: misconcept… Chris Lewis
- Re: [Asrg] misconception in SPF Alessandro Vesely
- Re: [Asrg] whitelisting links (was Re: misconcept… Paul Smith
- Re: [Asrg] whitelisting links (was Re: misconcept… Martijn Grooten
- Re: [Asrg] misconception in SPF Martijn Grooten
- Re: [Asrg] whitelisting links (was Re: misconcept… Rich Kulawiec
- Re: [Asrg] whitelisting links (was Re: misconcept… Michael Thomas
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] whitelisting links (was Re: misconcept… John Johnson
- Re: [Asrg] misconception in SPF John Johnson
- Re: [Asrg] whitelisting links (was Re: misconcept… Michael Thomas
- Re: [Asrg] whitelisting links (was Re: misconcept… John Levine
- Re: [Asrg] misconception in SPF Dotzero
- Re: [Asrg] misconception in SPF John Levine
- Re: [Asrg] misconception in SPF Laura Atkins
- Re: [Asrg] DMARC, was misconception in SPF John Levine