# CVE-2026-53994: proftpd-dfsg: ProFTPD mod_sftp contains a heap-based buffer overflow reachable by an authenticated SFTP user

CVE-2026-53994 is fixed in proftpd-dfsg on 1 platform, first by DEBIAN-CVE-2026-53994, released July 20, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-53994
- Priority: Routine
- CVSS: 6.5 (medium)
- EPSS: 0.0045
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 18, 2026

## Description

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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | proftpd-dfsg Debian 13.5 (trixie) | 1.3.8.c+dfsg-4+deb13u3 | [DEBIAN-CVE-2026-53994](https://patchblox.com/security/data/fix/linux/debian-cve-2026-53994.md) | Jul 20, 2026 |
| Linux | proftpd-dfsg Debian 14 | 1.3.9b~dfsg-1 | [DEBIAN-CVE-2026-53994](https://patchblox.com/security/data/fix/linux/debian-cve-2026-53994.md) | Jul 20, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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