# FTP transfers of files smaller than 1KB fail and result in empty files on destination server

**Product**: Other  
**Version**: R81.10 (EOS), R81.20  
**Last Modified**: 2026-07-23

## Symptoms

- Files smaller than 1KB transferred via FTP are received as empty files (0KB).
- FTP clients such as FileZilla display errors like " _File transfer aborted by user for small files_".
- The FTP server responds with " _150 Ok to send data_", but the resulting file on the destination is empty.
- Debug logs show ADVP errors with messages such as " _allowed writing size: 0 bytes_" for small files.

## Cause

The Stateful Inspection engine incorrectly sets a variable controlling the transfer buffer size to 0 when the file size is smaller than 1024 bytes (the default value).

The conditional statement in the code blocks the transfer of small files. Larger files are unaffected because their longer transfer duration allows proper connection setup before the buffer size is evaluated.

## Solution

This problem was fixed. The fix is included in:

- [Jumbo Hotfix Accumulator for R82.10](https://sc1.checkpoint.com/documents/Jumbo_HFA/R82.10/Default.htm) starting from Take 36
- [Jumbo Hotfix Accumulator for R82](https://sc1.checkpoint.com/documents/Jumbo_HFA/R82/Default.htm) starting from Take 118
- [Jumbo Hotfix Accumulator for R81.20](https://sc1.checkpoint.com/documents/Jumbo_HFA/R81.20/Default.htm) starting from Take 158

If you choose not to upgrade, Check Point can supply a **Hotfix**. [Contact Check Point Support](https://www.checkpoint.com/support-services/contact-support/) to get a Hotfix for this issue.

A Support Engineer will make sure the Hotfix is compatible with your environment before providing the Hotfix.

For faster resolution and verification, please collect [CPinfo files](http://supportcontent.checkpoint.com/solutions?id=sk92739) from the Security Management Server and Security Gateways involved in the case.

**Hotfix installation instructions:**

Refer to [sk168597 - How to install a Hotfix](https://support.checkpoint.com/results/sk/sk168597).

#### NOTE

This solution has been verified for the specific scenario, described by the combination of Product, Version and Symptoms. It may not work in other scenarios.

## Article Properties

**Access Level**: General  
**Status**: Approved by TAC  
**Date Created**: 2025-10-20  
**Last Modified**: 2026-07-23