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From e-mail to telephone quantity, a brand new OSINT method

From e-mail to telephone quantity, a brand new OSINT method

2023-11-16 09:20:52

These days I’ve been spending time researching weaknesses and assault vectors in password reset choices. At BSides Las Vegas I presented a tool called “Ransombile”. It automates the password reset course of over SMS for a lot of Alexa high 100 web sites and facilitates focused assaults when having bodily entry to locked cell gadgets for a brief time period. I’ve also talked about the wide impact of compromising voicemail systems at DEF CON and CCC by abusing password reset over telephone calls.

Whereas engaged on these subjects, I spent many hours testing and resetting passwords in varied completely different web sites. In some unspecified time in the future, I began noticing a sample I hadn’t observed earlier than. Once you need to reset a password, you enter the e-mail and are then introduced with completely different choices. These often embrace receiving an e-mail with a novel hyperlink to click on on, getting an SMS with a secret six digit code and even the choice to obtain a name and listen to the key code as an alternative.

Whereas reviewing the choice of resetting a password with both an SMS or telephone name, I observed that the UI often exhibits a part of the telephone quantity. Nonetheless it’s masked in a manner that it’ll reveal just a few digits, sufficient for the person to acknowledge which one in case he has a number of telephones. In different phrases, if I do know your e-mail, I can provoke the password reset course of to your accounts and procure a number of digits of your telephone quantity.

As talked about above, I’ve spent a variety of time resetting passwords and I spotted that not all web sites reveal the identical digits. Some would present the final 4, some would present the primary one, the final two and so forth. There isn’t a customary solution to masks private identifiable info (PII) akin to telephone numbers. The masking occurs solely on the builders discretion and that appeared like an issue to me.

Password reset shows 5 digits
Password reset exhibits 5 digits
2FA shows 3 digits
2FA exhibits 3 digits

To show to which extent that is the case, take Paypal for instance. If I provoke the password reset course of, it is going to reveal the primary digit and the final 4. However, if I login and get challenged with 2FA, it is going to reveal solely the final three. This doesn’t make any sense. With solely your e-mail deal with, I can get 5 of your ten digits telephone quantity. If I do know your e-mail and password, then I’ll solely get three. Paypal hides extra digits from an attacker that is aware of your password already than from one which solely is aware of your e-mail deal with.

Digging deeper

I made a listing of in style web sites that individuals are typically registered on and checked their password reset course of. My objective was to establish which internet sites would solely ask for an e-mail to provoke the method (no additional info wanted), supported cell based mostly password reset and variety of digits “leaking”. Here’s a small subset:

Leaks first three and final two digits:

Leaks first and final 4 digits:

Leaks first and final two digits:

Leaks final 4 digits:

Leaks final two digits:

  • Google
  • Fb
  • Twitter
  • Hotmail
  • Steam

In the event you have a look at the listing above, we are able to conclude that, for instance, when you have an eBay and a LastPass account, an attacker can know seven out of ten digits of your telephone quantity. Simply by understanding your e-mail deal with. In different phrases, an attacker can use your e-mail deal with to scale back the chances of guessing your telephone quantity from one billion potentialities to at least one thousand.

This isn’t the one mixture doable however let’s concentrate on this state of affairs on this publish.

Discovering the remaining numbers

We have now seven out of ten digits which implies we’re solely lacking three. At this level, it is very important concentrate on which numbers we all know.

A US telephone quantity consists of three fields: space code (or NPA), change (or Central Workplace Code) and subscriber quantity (kudos to @jjarmoc who advised me in regards to the change and made me notice there was extra to this than I believed). There’s additionally the nation code however we’re specializing in US numbers for now.

US phone number fields
US telephone quantity fields

eBay+LastPass gave us the world code and the subscriber quantity. It is very important spotlight that we aren’t merely lacking 3 digits, we’re lacking the three digits equivalent to the change. This is a crucial distinction as it is going to assist us slim down the chances even additional.


I put fairly plenty of hours researching and studying about exchanges. My fundamental objective was to know if I might reliably scale back the remaining thousand doable telephone numbers by detecting change numbers not assigned to a particular space code.

Enter the North American Numbering Plan Administrator (NANPA). The numbering plan for the general public switched phone community for Canada, the US and its territories, and a few Caribbean nations. This web site is a goldmine! I discovered a lot about how the phone programs work simply from this supply. Most significantly, I discovered precisely what I used to be searching for.

NANPA maintains an up to date listing of space codes and the corresponding exchanges that is publicly accessible. It’s up to date ceaselessly and you may question the info or obtain a parseable file with all the data.

Exchanges in San Francisco
Exchanges in San Francisco

How helpful is that this? Effectively, let’s take San Francisco’s 415 space code. If I’m solely lacking the three digits equivalent to the change, I’ve a thousand doable numbers for my goal. Through the use of NANPA dataset, I decreased it to 784 doable numbers as a result of there are 216 change quantity not assigned to 415 space code. That could be a discount of over 20%, not unhealthy!

However how good does it get? I performed with completely different space codes and, for instance, the Alaska 907 space code has solely 625 exchanges assigned. That’s 375 telephone numbers we don’t want to contemplate anymore by simply utilizing the precious info that NANPA gives us. Or Tacoma’s 253 space code with solely 458 exchanges. We removed over half the doable telephone numbers.

What if the goal solely has a Paypal account? We all know 5 out of ten digits. However once more, which ones? We have now the primary digit of the world code and the final 4 random digits. Let’s think about that the goal is from California. Due to NANPA, we all know all the world codes equivalent to California. There are solely two space codes in California that begin with 2, 213 and 209. Different two that begin with 3, two that begin with 4, and so on. By understanding the primary digit of the world code, you may nonetheless infer the primary three digits of the telephone quantity pretty simple.

Nationwide Pooling Administration

However how about if the goal solely has an eBay account? Or Paypal + Google? We have now the world code and the final two digits of the subscriber quantity. Once more, let’s concentrate on which numbers we all know. I mentioned above how we are able to use NANPA’s public information to slim down doable numbers based mostly on the world code and the change. Are there any public information that may assist us discard invalid telephone numbers based mostly on the subscriber quantity? Sure! Due to the national pooling administration.

Prepared? Quantity pooling is a solution to assign smaller blocks of numbers (within the hundreds) to development areas. Traditionally, a telephone quantity is a manner of rooting a name to an individual in a bodily location. Take 415-272-XXXX. The primary 3 digits slim it all the way down to a wider space like San Francisco, the 272 change is particular to Sausalito and the lacking 4 digits specify the precise individual (subscriber) in that restricted space. As a result of carriers personal the precise space code + change, which means there space 10000 telephone numbers assigned to Sausalito residents which have a plan with AT&T (the provider proudly owning 415-272).

As of 2017, Sausalito has 7110 residents. Which means that from the 10k out there numbers, solely 7k will likely be used, and that if everyone seems to be an AT&T buyer. With this fashion of assigning numbers, many are going to waste and won’t be used.

The irruption of cable modems and VOIP companies which made it simpler to change into a provider worsened the issue. The FCC decided that numbers should be assigned in smaller blocks in growth areas. Particularly in blocks of thousand numbers quite than ten thousand. Due to this fact, blocks of numbers could be assigned as XXX-XXX-X to carriers, together with the primary digit of the subscriber quantity.

The nationwide pooling administration is liable for managing it and has public records of the assigned blocks, together with the subscriber digit. We are able to use this information to additional discard invalid numbers. For instance, taking our Sausalito quantity 415-272-XXXX which is lacking the final 4 digits, we are able to use the general public information to discard telephone numbers like 415-272-[0-8]XXX and focus simply on numbers which subscriber begins with 9. In different phrases, we now have decreased the doable legitimate telephone numbers from 10 thousand to at least one thousand.

9th block is the only one assigned
ninth block is the one one assigned

Nonetheless… many doable numbers remaining

You’ve got your goal’s e-mail deal with who occurs to be from Tacoma and has an eBay and LastPass account. You provoke the password reset course of and harvest seven out of ten digits of his telephone quantity. Now, you need to use NANPA to do away with 542 and scale back the listing to 458 doable numbers assigned to that e-mail deal with. You then use the Nationwide Pooling Administration to examine if the block quantity yo have is assigned to the completely different doable exchanges decreasing the doable legitimate telephone numbers to 445.

What now? It’s nonetheless a good quantity of telephone numbers. I’d declare that decreasing one billion doable telephone numbers all the way down to 445 solely understanding an e-mail is fairly vital. The rest might even be examined manually. However the objective is to scale back the chances as a lot as doable earlier than making an attempt any handbook verification. Let’s return to the drafting board!

There’s plenty of methods you possibly can take the remaining telephone numbers and see if they’re in some way linked to the e-mail deal with. Utilizing search engines like google and yahoo with properly outlined search flags to strive discover clues in case the goal left his telephone quantity in a discussion board, web site, and so on. Look the e-mail up by telephone quantity on on-line companies like pipl, BeenVerified or Spokeo which have enormous databases with folks’s private info. You may even use phone system on-line companies that assist you to reverse search the proprietor of a telephone by its quantity. Principally, a phonebook in reverse. I used to be really fairly shocked by the quantity of private info I used to be in a position to get from companies like WhitePages via it’s Twilio add-on by simply offering a telephone quantity and pay ten cents.

These choices are good however not 100% dependable. Chances are you’ll not discover something in search engines like google and yahoo, on-line information farms don’t have your goal’s telephone quantity and WhitePages tends to be considerably outdated, many occasions it simply doesn’t have the data you want. So, I began to think about new methods I might reliably receive the telephone quantity assigned to an e-mail deal with.

Reusing the identical assault vector, in reverse

It didn’t take lengthy to get to that candy “Eureka” second. I mirrored on the steps I took to get this far. I used to be abusing the password reset perform of on-line companies to gather just a few telephone quantity digits assigned to an e-mail…

Hmmm.. I reset the password placing an e-mail… and I get just a few digits again. Can I… reset the password by coming into a telephone quantity and get just a few e-mail characters again?

Amazon password reset using phone number
Amazon password reset utilizing telephone quantity

Eureka! Seems, there are in style companies, like Amazon and Twitter, that assist you to reset the password by coming into a telephone quantity and get an e-mail to finish the method. Most significantly, it is going to show just a few characters of the e-mail deal with it is going to ship the hyperlink to. In Amazon’s case, you get the primary and final letter of the username and the complete area. You additionally get the size of the username because the variety of * matches the variety of masked chars.

Twitter exhibits you the primary two characters of the username and the primary one of many area. You additionally will know the size by counting the asterisks.

The assault vector appears like this:

1. Use the goal’s e-mail deal with to provoke the reset password course of in a number of websites to reap a number of telephone quantity digits

2. Cut back the doable telephone quantity listing by discarding non-existing space codes, exchanges and subscriber numbers utilizing NANPA and the Nationwide Pooling Administration publicly out there information

3. Provoke the password reset course of iterating over the rest telephone quantity listing and correlate the leaked e-mail chars towards the goal’s e-mail deal with

By following these steps, it is possible for you to to acquire the complete ten digit telephone quantity related to the e-mail deal with, with out having to make one single name! Simply by abusing password reset choices and bruteforcing effectively utilizing publicly out there info.


The assault vector above might be achieved manually. You can use services like namechk to pinpoint where to go harvest digits. Have a look at NANPA’s information your self to discard invalid numbers. You may even bruteforce the remaining telephone numbers to seek out the matching e-mail utilizing internet proxy options like Burp’s intruder. However you don’t must, I wrote a instrument that may do all this for you.

email2phonenumber is a instrument that lets you present a partial telephone quantity and get a listing of all of the doable legitimate telephone numbers, eliminating non-existing space code and change numbers. The instrument may even allow you to bruteforce telephone numbers utilizing Amazon’s and Twitter’s password reset characteristic and correlate the masked emails towards the one you supplied searching for a match. It’ll try to fly beneath the captcha radar by replicating person habits and randomizing some parameters within the requests. It additionally helps using proxy servers. What we’re doing is beginning the password reset for various telephone numbers. Which means that the companies can’t detect you based mostly on a particular telephone quantity you might be hammering on.

There are a number of different companies that permit password reset utilizing telephone numbers that can be utilized for a similar objective. The instrument helps Amazon and Twitter for bruteforcing. The concept is to get help from the group by way of pull requests to help further ones.

You will discover the instrument in my github repo.



email2phonenumber is a good instrument however a lot of what it does might be achieved with instruments like Burp or wfuzz. The true energy depends on the gathering, parsing and use of the general public out there information associated to a rustic’s telephone numbering plan.

See Also

Due to this fact, I’m engaged on a brand new on-line service that might permit you ti generate lists of doable telephone numbers. It’ll have multi-country help, it provides you with rather more info and particulars, it is going to have historic information and most significantly, superior filters.

Say the goal has AT&T, you may filter by provider and scale back the listing of doable numbers much more. You could have intel that the individual is from California, phonerator will keep in mind solely these space codes. Perhaps that the goal had the telephone quantity for over two years, so let’s discard exchanges and block numbers that had been assigned lately.

I’m nonetheless engaged on the instrument and accumulating all information. Please keep tuned for updates and launch dates on my twitter account. It’s lastly here!

Different nations

To date I’ve centered on US telephone numbers however there are further points I need to spotlight when contemplating targets from different nations. I’m from Spain myself and Spanish cell phone numbers have attention-grabbing properties as properly. For starters, all cell phone numbers begin with the digit 6 (and lately 7). Additionally, telephone numbers are solely 9 digits lengthy. Why is that essential? Effectively, I do know one digit from the start and companies like eBay or LastPass don’t regulate their masks to leak much less digits for shorter telephone numbers. Due to this fact, if my goal is from Spain, simply with LastPass I do know 5 out of the 9 digits. That’s over half the digits.

I’ve noticed the issue of utilizing the identical masks for all clients in different web sites as properly. My subsequent step was to search for nations that had very quick numbers. Take Iceland, Estonia or San Salvador with 7 digit telephone numbers. All eBay clients from these nations have 5 out of seven digits uncovered to anybody that is aware of their e-mail deal with. Mix it with LastPass accounts and you bought your self the goal’s full telephone quantity. Simply by understanding their e-mail deal with…

By understanding the properties of a rustic telephone quantity system and benefiting from web sites that don’t regulate their masking to leak much less digits on shorter numbers, it’s doable to reap all digits of the telephone quantity.

So what?

I confirmed you the way to go from an e-mail deal with to a telephone quantity. So what? Is that actually so unhealthy? Effectively, we are able to reply this query from completely different angles like privateness and safety however let’s listing plenty of assault vectors that originate from the information of a goal’s telephone quantity:

  • SIM swapping. This is a matter that gained a variety of notoriety these days and it is more common than you might think. Attackers are in a position to port your telephone quantity to a SIM of their management by completely different means like social engineering, extortion and even rogue provider staff. This is able to permit the attackers to reset passwords in your behalf or bypass 2FA protections.
  • SS7 assaults. SS7 is a protocol utilized by carriers to work together amongst them. It is extremely outdated and researchers have demonstrated at a number of safety conferences how they will observe the placement of people, and even spy on communications.
  • Concentrating on your voicemail. Take a look at my DEF CON talk to know the affect of getting an attacker compromise your voicemail. Severely, voicemail systems are a threat.
  • Location monitoring. Joseph Cox has achieved a great coverage of this issue.
  • CallerID spoofing. Loads of on-line companies assist you to spoof caller IDs. This can be a useful gizmo for social engineering.


The shortage of a standardized solution to masks PII results in completely different approaches taken by on-line companies. These are leaking partial details about your e-mail deal with and telephone quantity in locations just like the reset password space. It may be abused and automatic to scrape items of data with the intent of reconstructing the focused information.

It’s doable, specifically on focused assaults, to acquire all digits of a telephone quantity related to an e-mail deal with. As soon as the attacker is in possession of the telephone quantity, he can use it for different assaults with severe affect that may result in full account compromise, location monitoring and spying.

That is specifically true in nations with shorter telephone numbers, as many companies don’t regulate their masking to the telephone size.

Masking isn’t ok, even when it simply exhibits a few the telephone quantity’s digits. Inhabitants of Saint Helena deserve the identical safety bar as the remainder of us with their 5 digits long phone numbers. For emails, masking solely the username isn’t ample, the area can present details about the place that individual may match. Even the TLD may give away if that individual is a pupil or from which nation they could be.

My proposal is to permit customers to set labels. For instance, the person can label an e-mail deal with as “private e-mail” or the telephone quantity as “work telephone”. This fashion, when the password reset course of shows a touch, it is going to present the label quite than tidbits of PII.

Customers mustn’t present their telephone quantity until strictly required. Many on-line companies ask for it however there isn’t a actual enterprise want. They simply need extra details about you. If it’s a requirement, think about using a digital quantity like Google Voice or perhaps a devoted SIM that you simply solely use for this objective and by no means give the quantity away.

This isn’t nearly OPSEC, it’s about retaining your information safe.

Accountable disclosure

I reached out to the net companies that had been displaying greater than 2 digits, particularly in the event that they had been a part of the world code or change. LastPass up to date the masks to simply present the final two digits equivalent to the subscriber quantity. eBay is displaying now the primary and final two digits, not nice however higher than it was earlier than. Yahoo remains to be contemplating dangers and mitigations as of this writing.

Paypal, which shows 5 digits together with space code to anybody understanding the e-mail deal with (however solely three if the attacker is aware of the goal’s password), determined that is working as designed and won’t take motion.


I introduced this analysis at BSides Las Vegas and the Recon Village @ DEF CON

You may download the slides from slideshare

Exploding the Phone: The Untold Story of the Teenagers and Outlaws Who Hacked Ma Bell by Phil Lapsley

Incredible e book throughout telephone phreaking.

The privacy, security & OSINT show – Episode  111

This explicit episode talks in regards to the problems with offering your telephone quantity to on-line companies.

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