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This bounty program is for the FileZilla Client and the libfilezilla library

Disclosure Policy

  • Follow HackerOne's disclosure guidelines.
  • Let us know as soon as possible upon discovery of a potential security issue, and we'll make every effort to quickly resolve the issue.
  • Please provide detailed reports with reproducible steps demonstrating a plausible exploitation scenario, if the report is not detailed enough to reproduce the issue, the issue will not be eligible for a reward.
  • Multiple vulnerabilities caused by one underlying issue will be awarded one bounty.
  • The project maintainers have final decision on which issues constitute security vulnerabilities.


While researching, we'd like to ask you to refrain from:

  • Denial of service
  • Spamming
  • Social engineering (including phishing) against anybody associated with the FileZilla project
  • Any physical attempts against the property of the FileZilla project and its members.


The bug bounty program will test only:

All reported bugs must have a security impact. If you encounter ordinary bugs without security impact, please report them on https://trac.filezilla-

(Note: A separate bounty program for FileZilla Server may be creatd in the future)

Out of Scope

  • Outdated versions of the software
  • Services running on the and domains and their subdomains
  • Exploits which rely on the assumption that the attacker already has access to the user account FileZilla is run under on the victims system.
  • "Layer 8" issues. Always assume the user is making informed decisions if he is given the information to do so.

The following components are also explicitly not in the scope:

  • The src/storj sub-directory of FileZilla and the libstorj dependency
  • The src/putty sub-directory of FileZilla contains a modified code from PuTTY. Issues inherited from PuTTY are not in scope. Note: Issues in the modifications specific to FileZilla still are in scope.

Submission guidelines

While FileZilla is cross-platform, vulnerabilities are to be evaluated given contemporary computer architectures.

Submissions must include either:

  • A detailed explanation explaining the vulnerability based on the source code
  • Simple steps to reproduce the vulnerability without requiring the reproducing party to use specialized tools
  • A proof-of-concept (PoC)

FileZilla technical overview

Building FileZilla

FileZilla uses the GNU autotools as build system.

It, as well as almost all its dependencies, can be built using the familiar configure && make && make install trinity.

The following two guides have recently been updated and can be used to build FileZilla:


FileZilla directly depends on the following libraries:

  • libfilezilla : base library for many things such as networking, file i/o, string utilities and the main event system
  • wxWidgets : GUI framework
  • GnuTLS : TLS
  • Nettle : Various cryptographic functions used e.g. for the master password functionality
  • pugixml : DOM-style XML parser. XML is used to store settings
  • SQlite : SQL database, used to persist the transfer queue


FileZilla is organized in different components. The most important components are, identified by subdirectory:

  • src/engine: The protocol implementations
  • src/engine/ftp: FTP specific functionality
  • src/engine/sftp: SFTP specific functionality, wraps around fzsftp
  • src/engine/http: Everything specific to HTTP functionality
  • src/interface: The user interface and controlling logic such as the transfer queue
  • src/putty: Source for fzsftp, a heavily modified version of PuTTY's psftp
  • src/fzshellext: The Windows shell extension to facilitate Drag&drop from Explorer into FileZilla.

Interesting places

Due to their importance or complexity, we think these parts of the code warrant a closer look:


  • src/engine/directorylistingparser.cpp: The directory listing parser in
  • src/interface/updater.cpp: The update mechanism
  • src/engine/http/request.cpp: The HTTP state machine capable of request pipelining


  • tls_layer_impl::verify_certificate in lib/tls_layer_impl.cpp: Certificate verification
  • lib/encryption.cpp: The asymmetric encryption scheme used for the master password functionality


Our rewards are based on the severity of a vulnerability. HackerOne uses CVSS 3.0 (Common Vulnerability Scoring Standard) to calculate severity.

critical | 9.0 - 10.0 | $5000
High | 7.0 - 8.9 | $2500
Medium | 4.0 - 6.9 | $1000
Low | 0.1 - 3.9 | $250

Examples for vulnerabilities

Critical severity bugs - $5000

  • Remote Code Execution over an unauthenticated channel

High severity bugs - $2500

  • Code Execution over an authenticated channel
  • Information leaks of private data such as file contents

Medium severity bugs - $1000

  • Remotely triggered crashes
  • Remotely triggered infinite loops

Low severity bugs - $250

  • Memory leaks
  • Crashes as result of user action
  • User-initiated infinite loops

No reward for leak of public information:

  • File names, their sizes and modification times

Safe Harbor

Any activities conducted in a manner consistent with this policy will be considered authorized conduct and we will not initiate legal action against you. If legal action is initiated by a third party against you in connection with activities conducted under this policy, we will take steps to make it known that your actions were conducted in compliance with this policy.

If you have any questions or concerns on this challenge, please contact

Thank you for helping keep FileZilla and our users safe!

In Scope

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Out of Scope

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Firebounty have crawled on 2019-11-08 the program FileZilla on the platform Hackerone.

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