---
id: CVE-2026-53994
title: >-
  ProFTPD mod_sftp contains a heap-based buffer overflow reachable by an
  authenticated SFTP user
summary: >-
  ProFTPD mod_sftp contains a heap-based buffer overflow reachable by an
  authenticated SFTP user. The fxp_packet_read() function accepts the
  attacker-supplied 32-bit big-endian SFTP packet length without a minimum
  sanity check. A value of …
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-122
published: '2026-07-18'
updated: '2026-07-18'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-53994'
references:
  - url: 'https://github.com/proftpd/proftpd'
    label: disclosure@vulncheck.com
  - url: >-
      https://github.com/proftpd/proftpd/commit/7342836fa98e36209660a4c5805c801476f63936
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/proftpd-mod-sftp-heap-buffer-overflow-via-unsigned-integer-underflow-and-size-truncation
    label: disclosure@vulncheck.com
tags:
  - nvd
ingestedAt: '2026-07-19T08:30:39.929Z'
epss: 0.00747
epssPercentile: 0.52901
---

## Overview

ProFTPD mod_sftp contains a heap-based buffer overflow reachable by an authenticated SFTP user. The fxp_packet_read() function accepts the attacker-supplied 32-bit big-endian SFTP packet length without a minimum sanity check. A value of 0 causes an unsigned subtraction elsewhere in the read path to underflow to approximately 4 GB. That oversized request reaches the core memory allocator, where the rounded size is computed in size_t but passed to new_block() as a 32-bit int; the low 32 bits of 0x100000000 are 0, so new_block() returns a small (~512-byte) block while the caller is told it received ~4 GB. The subsequent fill loop then streams attacker-controlled bytes past the end of the 544-byte allocation, producing an attacker-controlled heap buffer overflow. An authenticated user can crash the per-connection ProFTPD session child on demand with a single malformed SFTP packet (packet_len=0 followed by a body greater than approximately 544 bytes), producing reliable authenticated remote denial of service. Depending on heap layout and adjacent allocations, heap metadata corruption and further consequences beyond denial of service may be possible, though only denial of service is demonstrated by the supplied proof of concept.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.