Vulnerability · Published Jul 20, 2026 · Assigned by VulnCheck

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

Medium 6.5

In plain English

A medium-severity integer overflow in proftpd from proftpd. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 45% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)6.5Medium

Exploit odds (30 days)0.5%top 55.3% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	proftpd-dfsg	no fix listed	DEBIAN-CVE-2026-63091
Debian:13	proftpd-dfsg	1.3.8.c+dfsg-4+deb13u3	DEBIAN-CVE-2026-63091
Debian:14	proftpd-dfsg	1.3.9c~dfsg-1	DEBIAN-CVE-2026-63091
Ubuntu:22.04:LTS	proftpd-dfsg	no fix listed	UBUNTU-CVE-2026-63091
Ubuntu:24.04:LTS	proftpd-dfsg	no fix listed	UBUNTU-CVE-2026-63091
Ubuntu:26.04:LTS	proftpd-dfsg	no fix listed	UBUNTU-CVE-2026-63091
Ubuntu:26.10	proftpd-dfsg	no fix listed	UBUNTU-CVE-2026-63091

Affected products (as reported)

Vendor	Product	Versions
proftpd	proftpd	0 – before 1.3.9c1.3.10rc1 – before 1.3.10rc3

Weakness: CWE-190, CWE-126 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

References

Release Notes release-notes
ProFTPD 1.3.10rc3-3 Release Notes patch, release-notes
ProFTPD 1.3.9c Release Notes patch, release-notes
Pull Request issue-tracking, patch
Patch Commit patch
https://www.vulncheck.com/advisories/proftpd-mod-sftp-signed-integer-overflow-via-scp-size-record-parser third-party-advisory