Security Issue Reporting
Security issue reporting guidelines
If you think you have found a security vulnerability in Fastmail, please report it to us straight away by emailing security@fastmailteam.com. Please include detailed steps to reproduce and a brief description of what the impact is. We encourage responsible disclosure (as described below), and we promise to investigate all legitimate reports in a timely manner and fix any issues as soon as we can.
We do read all reports within 24 hours, but as all reports are reviewed and personally investigated by our senior staff, it may take up to 10 business days before you hear back from us.
Responsible disclosure policy
We ask that during your research you make every effort to maintain the integrity of our users’ data, avoiding violating privacy or degrading our service. You must give us reasonable time to fix any vulnerability you find before you make it public. In return we promise to investigate reports promptly and not to take any legal action against you.
Bug bounty
Our bug bounty program is common to all products produced by Fastmail, and thus covers our Topicbox and Pobox products in addition to our flagship Fastmail service.
As a measure of our appreciation for security researchers, we are happy to give full credit in any public postmortem after the bug has been fixed, and we offer a monetary bounty for certain qualifying bugs. To qualify for the bounty, you must:
- Follow our responsible disclosure policy (see above).
- Report the bug to us first, and give us reasonable time to fix the issue before making it public.
- Be the first person to report the issue to us.
- Use a test account (a free trial account is fine), or an account that you control. Never interact with other accounts without the owner’s consent.
- Find a bug that could allow access to private user data, or enable access to a system running Fastmail infrastructure.
Examples of valid vulnerability types include:
- Authentication or session management issues
- Cross-Site Scripting (XSS) (only on
www.fastmail.com or beta.fastmail.com, not on user.fm or fastmailusercontent.com; see below) - Cross-Site Request Forgery (CSRF/XSRF)
- Remote Code Execution
- Privilege Escalation
The decision of whether a bug qualifies for a bounty is solely at the discretion of Fastmail. Any qualifying bug will be eligible for a bounty of a minimum of US$100 and a maximum of $5,000. The exact value will be determined by Fastmail after taking into account the severity of the vulnerability, the number of users potentially affected etc. All bounties will be paid via PayPal. Any taxes or fees are the sole liability of the recipient. We process bug bounty payments once a month.
Specific exclusions
People seem to report these regularly, so we’re putting them up front to make it clear we do not regard these as bugs
- Email spoofing bugs do not qualify. We are quite aware that users can set arbitrary From addresses on emails, that our SPF records allow arbitrary hosts to send email as our domains, and that our DMARC policy is not enforcing passes. These policy decisions are by design, and we track the actual sender in a separate header.
- CSV Excel Macro Injection bugs via address book exporting do not qualify. The user has complete control over their address book. We regard convincing someone to add a particular address to their address book, export and download it as a CSV, open it in Excel, click through a warning dialog as exceedingly unlikely user interaction. If you can get them to do that, just get them to run cmd from the Start menu and paste some arbitrary command.
General Exclusions
- Denial of Service (DOS) and social engineering attacks do not qualify and must not be attempted against Fastmail or our users under any circumstances.
- Bugs that require exceedingly unlikely user interaction or are caused by insecurities in browser extensions do not qualify.
- Brute force log in attempts.
- The domains
user.fm and fastmailusercontent.com are used to host potentially unsafe user content. By keeping this content in completely separate domains, we avoid any security issues with our corefastmail.comdomain. As such, any Cross-Site Scripting (XSS) attacks on these sites are not of interest to us. Please note that if you go to a user web site such as testuser.fastmail.com it immediately redirects to testuser.fastmail.com.user.fm and is thus in theuser.fmsecurity domain, not the fastmail.com domain. - Bugs on sites associated with Fastmail but not run by Fastmail do not qualify. This includes www.fastmailfbl.com. We are grateful for any reports on issues with these sites, and we will pass on the bugs to the relevant company, however they do not qualify for a bounty.
- Anything related to enumeration of usernames does not qualify.
- Bugs related to unpatched, out of date or exceedingly rarely used browsers or other client software out of our control.
- We are public about the software we run. We are not interested in reports about “leakage” of the fact we run nginx, or the version number, or Perl module names or file paths.
Hall of fame
Our thanks to the following security researchers for their submissions:
2025
| Researcher | Vulnerability found | Bounty paid |
| Lyra Rebane (rebane2001) | Multiple CSS sanitisation bypasses | $2500 |
| Mohsin Ali | Topicbox firewall misconfiguration | $500 |
| Jaikishan Tulswani | Internal documentation leak | $200 |
2024
| Researcher | Vulnerability found | Bounty paid |
| Amethama Luturmas | Topicbox ACL bypass | $100 |
2023
| Researcher | Vulnerability found | Bounty paid |
| Mohammad Eldawody | Fastmail 2FA vulnerability | $3000 |
| Max Raams | Email authentication weaknesses | $250 |
2022
| Researcher | Vulnerability found | Bounty paid |
| Vivek Kumar Yadav | Topicbox app vulnerability | $100 |
| Vivek Kumar Yadav | Android app vulnerability | $100 |
| Milan Jain | CRLF injection vulnerability | $250 |
| Ilkin Javadov | Pobox password link expiry | $100 |
| Huzaifa Muhammad | Topicbox mobile app vulnerability | $100 |
| Huzaifa Muhammad | Anti-abuse bypass on mobile app | $100 |
| Jonathan Page | DKIM oversigning | $200 |
2021
| Researcher | Vulnerability found | Bounty paid |
| Dennis Trappe | iOS app vulnerability | $100 |
| Sheikh Rishad | Android app vulnerability | $100 |
| Jaikishan Tulswani | Access vulnerability for third party service | $250 |
| Mohammed Eldawody | Bypass security screen in Topicbox | $100 |
| Vicky Sahputra | Deleted group vulnerability in Topicbox | $100 |
| Markus Holtermann | Fingerprint authentication vulnerability in Fastmail app | $100 |
| N Krishna Chaitanya | Password reset vulnerability in Pobox | $100 |
| Pravas Ranjan Kanungo | Image proxy vulnerability in Fastmail | $100 |
| Mohammed Eldawody | Password recovery bug in Pobox | $3000 |
| Roman Zabaluev | Caching of “don’t require 2FA again on this device” cookie validity | $500 |
2020
| Researcher | Vulnerability found | Bounty paid |
| Mohammed Eldawody | Privilege escalation bugs in Topicbox | $2000 |
| Mohammed Eldawody | Bypass security screen in Topicbox | $200 |
| Daniel Santos | Mutation bypass in DOMPurify | $100 |
| Michał Bentkowski (Securitum) | CSS sanitisation bypass | $750 |
| Michał Bentkowski (Securitum) | DOMPurify mXSS (sponsored bug bounty; did not affect Fastmail products) | $250 |
| Mohammed Eldawody | Stored XSS in Pobox | $200 |
| Mart Gil Robles | Login CSRF in Pobox | $100 |
| Basavaraj Banakar | Self-XSS in Pobox | $100 |
| Alexander Harkness | Unnecessary information disclosed in DMARC report | $100 |
| Jackson K V | Login rate-limiting bypass in Pobox | $200 |
| Sachin Hodkasia | Login rate-limiting bypass in Pobox | $200 |
| Sachin Hodkasia | Password reset expiration issue in Pobox | $100 |
| Syed Muhammad Asim | Mixed content warnings in Pobox | $100 |
2019
| Researcher | Vulnerability found | Bounty paid |
| Ace Candelario | HTML injection vulnerabilities in Pobox | $100 |
| Hemant Singh Manral | Limited reuse of expired recovery options | $250 |
| Joran Dirk Greef (Ronomon) | AppCache exploit to compromise attachment downloads | $3500 |
| Michał Bentkowski (Securitum) | DOMPurify mXSS (sponsored bug bounty; did not affect Fastmail products) | $500 |
| Joran Dirk Greef (Ronomon) | Bypasses to allowed attachment extensions | $200 |
| Devansh Batham (Infoziant Labs) | Deauthentication issue in Pobox | $100 |
| Devansh Batham (Infoziant Labs) | Password reset design issue in Pobox | $100 |
| Brian Hyde | HTML injection and email address injection vulnerabilities in Pobox | $400 |
| Jaikishan Tulswani | Session invalidation logic error in Pobox | $100 |
| Aman Mahendra | Race condition in 2FA login in Pobox | $100 |
| Devansh Batham (Infoziant Labs) | Miscellaneous CSRF vulnerabilities in Pobox | $500 |
| Devansh Batham (Infoziant Labs) | Request replay issue in Pobox | $200 |
| Anonymous | Incomplete access control restrictions on shared file storage within an account | $1000 |
| Aakash Kumar | Recovery code logic error in Pobox | $100 |
2018
| Researcher | Vulnerability found | Bounty paid |
| Devansh Batham (Infoziant Labs) | Password reset logic error in Pobox | $100 |
| Ahmed Elsobky | Phishing protection bypass | $100 |
| Tarun Mahour | Self-XSS in Pobox | $100 |
| Devansh Batham (Infoziant Labs) | CSRF vulnerabilities in Listbox | $200 |
| Anonymous | Network misconfiguration | $2000 |
| Nikola Kojic | Image proxy bypass | $100 |
| Jaikishan Tulswani | Page invalidation logic error in Pobox | $100 |
| Jaikishan Tulswani | Private services discovered | $100 |
| Jaikishan Tulswani | Session invalidation logic error in Listbox | $100 |
| Jaikishan Tulswani | List name discovery in Listbox | $100 |
| Aman Mahendra | Self-XSS in Listbox | $100 |
| Arsiadi Sriyanto | CSRF Token Disclosure | $100 |
| Aman Mahendra | XSS in Listbox | $200 |
| Jaikishan Tulswani | Page invalidation logic error | $100 |
| Jaikishan Tulswani | DNS misconfiguration | $200 |
| Jaikishan Tulswani | Open redirect in Listbox | $100 |
| Jaikishan Tulswani | Access control bypasses in Listbox | $700 |
| Jaikishan Tulswani | Multiple XSS and CSRF vulnerabilties in Listbox | $1000 |
| Aman Mahendra | links to insecure HTTP URLs provided in Listbox | $100 |
| Jaikishan Tulswani | CSRF in Listbox | $100 |
| Jaikishan Tulswani | subscription limit bypass in Listbox | $300 |
| Jaikishan Tulswani | access control bypass in Listbox | $100 |
| Ranjit Pahan | stored XSS in Listbox | $200 |
| Devansh Batham (Infoziant Labs) | UI redressing attack on Listbox and Pobox | $100 |
| Devansh Batham (Infoziant Labs) | Multiple XSS and CSRF vulnerabilities in Listbox and Pobox | $1200 |
| Brian Hyde | Multiple XSS and CSRF vulnerabilities in Listbox and Pobox | $1000 |
| Jaikishan Tulswani | XSS in Listbox | $200 |
| Bijan Murmu | Lax password policy in Listbox | $200 |
| Ranjit Pahan | window.opener phishing vulnerabilty with attachments | $100 |
| Chachi | Error in check preventing reuse of previous password | $100 |
| Jaikishan Tulswani | Session invalidation logic error | $100 |
| Jaikishan Tulswani | Referrer leakage from support ticket | $100 |
| Alex Zorin | Input truncation bypassing domain validation | $100 |
2017
| Researcher | Vulnerability found | Bounty paid |
| Max Justicz | Write access to server files | $4000 |
| Brian Hyde | Read-only access to private server files | $2000 |
| Arsiadi Sriyanto | Read access to private file storage metadata | $500 |
| Lucas Reddinger | Missing “enabled” check for shared calendar link | $500 |
| Bastian Welfrid Purba | CSRF in support ticket creation | $250 |
| Nikola Kojic | Image proxy bypass | $200 |
| Arsiadi Sriyanto | XSS on DAV subdomains | $200 |
| pnig0s | Unexploitable SSRF | $100 |
2016
| Researcher | Vulnerability found | Bounty paid |
| Arsiadi Sriyanto | Reflected XSS | $1500 |
| Brian Hyde | Server Side Request Forgery | $1000 |
| Shiv Bihari Pandey | Security settings unlock bypass | $500 |
| John Cleary | Incorrect CalDAV ACL check allowed access to list of unrelated users | $500 |
| Richard Smith | 2FA bypass when importing a user into a business | $300 |
| Shiv Bihari Pandey | SMS verification bypass | $250 |
| n00b 4lw4y5 7ry | Open redirect | $100 |
2015
| Researcher | Vulnerability found | Bounty paid |
| Salman Niksefat | XSS in email body (classic interface or old browsers only) | $1500 |
| Bogdan Calin | HTTP header injection | $500 |
| James Kettle (PortSwigger Web Security) | Login CSRF | $100 |
| Hugh Davenport | Deletion of contacts/events with restricted logins | $100 |
| Hugh Davenport | window.opener phishing vulnerabilty in classic interface | $100 |
2014
| Researcher | Vulnerability found | Bounty paid |
| Sergey Markov | Read-only access to private server files | $2000 |
| Thomas Guittonneau | Read-only access to private server files | $2000 |
| Sergey Markov | HTTP header injection | $1000 |
| Frans Rosén | XSS in email (classic interface only) | $1000 |
| Prashant Sharma | Stored XSS in our support ticket system | $1000 |
| Hammad Shamsi | Stored XSS in our support ticket system | $1000 |
| Bastian Welfrid Purba | Missing user privilege check for removing user websites | $1000 |
| Bastian Welfrid Purba | Missing user privilege check for fetching saved searches | $250 |
| Satish Bommisetty | Can trick user into making phone call in iOS app | $200 |
| Bastian Welfrid Purba | 4 self-XSS issues (not exploitable) | $400 |
| V. Harish Kumar | 2 self-XSS issues (not exploitable) | $200 |
| Ranjeet Singh | IMAP connections not immediately killed on password change | $100 |
| Sasi Levi | Self-XSS issue (not exploitable) | $100 |
| Manikandan Rajakumar | Self-XSS issue (not exploitable) | $100 |
| Lyon Yang | XSS in embedded image in email body (only classic interface, only IE6, only if remote images enabled) | $100 |
| Jakub Zoczek | HTTP header injection (only on redirect) | $100 |
| Rakesh Mane | Self-XSS issue (not exploitable) | $100 |
| Sasi Levi | CSRF on some business/family account admin actions | $100 |
| Sasi Levi | CSRF on some folder sharing actions | $100 |
| Hammad Shamsi | Open redirect in paypal handler | $100 |
| Mike Cardwell | Image proxying bypass on reply | $100 |
| Anonymous | window.opener phishing vulnerabilty | $100 |