# CVE-2026-63091: ProFTPD mod_sftp Signed Integer Overflow via SCP Size-Record Parser

> Authenticated attackers can trigger an integer overflow in ProFTPD's SFTP module to leak memory pointers, bypassing ASLR and facilitating further exploitation.

- **Severity:** High 7.1 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Jul 2026
- **Updated:** 28 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-63091, GHSA-gqm5-f386-9r92, UBUNTU-CVE-2026-63091

## What is CVE-2026-63091?

CVE-2026-63091 is a high-severity vulnerability in proftpd, published on 20 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official 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.

Weakness: CWE-190 (Integer Overflow or Wraparound), CWE-126 (Buffer Over-read)

## Which versions are affected by CVE-2026-63091?

It affects 1 product.


Products: Proftpd Proftpd.

## How do I fix CVE-2026-63091?

Upgrade to a fixed version.

## Is CVE-2026-63091 being exploited?

There is no known exploitation of CVE-2026-63091 in the wild and no public exploit code.

## Other vulnerabilities in proftpd

- [CVE-2010-4221](https://insights.sbomify.com/CVE-2010-4221/): Memory corruption in n/a (critical 10.0)
- [CVE-2010-20103](https://insights.sbomify.com/CVE-2010-20103/): ProFTPD 1.3.3c Backdoor Command Execution (critical 9.3)
- [CVE-2011-4130](https://insights.sbomify.com/CVE-2011-4130/): Use after free in n/a (critical 9.0)
- [CVE-2026-63090](https://insights.sbomify.com/CVE-2026-63090/): ProFTPD mod_sftp Heap Buffer Overflow via SFTP Packet Reassembly (high 8.7)
- [CVE-2026-35025](https://insights.sbomify.com/CVE-2026-35025/): ProFTPD ACL Bypass via /proc/self/root Path Prefix in RNFR (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63091 and fix it if it is affected.

What it is: CVE-2026-63091 is a high-severity vulnerability in proftpd, published on 20 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-63091 in the wild and no public exploit code.

Affected product: proftpd. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-63091/ (Markdown: https://insights.sbomify.com/CVE-2026-63091/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63091
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63091
- OSV: https://osv.dev/vulnerability/CVE-2026-63091

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63091/
Summaries are generated and may contain mistakes; the official description above is the record.