# CVE-2026-53994: ProFTPD mod_sftp heap buffer overflow in fxp_packet_read

Source: https://junglewise.ai/threats/cve-2026-53994-proftpd-mod-sftp-heap-buffer-overflow-in-fxp-packet-read  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-18. Updated: 2026-07-18  
License: CC BY 4.0 with a link back

CVE-2026-53994 · Severity: high · CVSS 7.5 · Published 2026-07-18

ProFTPD is a widely used file transfer server. A vulnerability in its SFTP module allows a logged-in user to crash the server session by sending a specially crafted data packet. While primarily resulting in a service outage for that user, this flaw could potentially lead to more severe system compromise depending on how the server's memory is organized.

## Quick answers

**Is CVE-2026-53994 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-53994 being exploited in the wild.

**How severe is CVE-2026-53994?** High severity, with a CVSS score of 7.5, published 18 July 2026.

**Which products and versions are affected?** ProFTPD Project ProFTPD < 1.3.10.

**Is there a fix for CVE-2026-53994?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-53994 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-53994?** Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A heap-based buffer overflow exists in the mod_sftp module of ProFTPD within the fxp_packet_read() function. The vulnerability is triggered when the function accepts an attacker-supplied 32-bit SFTP packet length of 0, leading to an unsigned integer underflow during size calculations. This results in a request for approximately 4GB of memory; however, due to an integer truncation when passing the size to the new_block() allocator as a 32-bit int, a small (~512-byte) buffer is actually allocated. Subsequent data reads then overflow this small buffer with up to 4GB of attacker-controlled data. While the primary impact is a reliable remote denial of service (crashing the session child process), heap metadata corruption may allow for more advanced exploitation. The issue is fixed in version 1.3.10.

## Affected products

- ProFTPD Project ProFTPD < 1.3.10

## Timeline

- 2026-07-18: disclosed
- 2026-07-18: advisory

## References

- [https://github.com/proftpd/proftpd](https://github.com/proftpd/proftpd)
- [https://github.com/proftpd/proftpd/commit/7342836fa98e36209660a4c5805c801476f63936](https://github.com/proftpd/proftpd/commit/7342836fa98e36209660a4c5805c801476f63936)
- [https://www.vulncheck.com/advisories/proftpd-mod-sftp-heap-buffer-overflow-via-unsigned-integer-underflow-and-size-truncation](https://www.vulncheck.com/advisories/proftpd-mod-sftp-heap-buffer-overflow-via-unsigned-integer-underflow-and-size-truncation)