CVE-2026-63091: ProFTPD before 1.3.9c and 1.3.10rc3 contains a signed integer overflow vulnerability in the mod_sftp module's

Q: How do I fix CVE-2026-63091?

proftpd: upgrade to 1.3.9c. Exact commands for each OS are on this page.

Q: Is CVE-2026-63091 being exploited?

CVE-2026-63091 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-63091 affect?

CVE-2026-63091 affects proftpd. Severity is medium (CVSS 6.5). 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 UI

Q: How urgent is CVE-2026-63091?

Priority 34/100. No elevated risk signals yet.

Routine

MEDIUM 6.5UPGRADE

CVE-2026-63091 is a medium-severity flaw (CVSS 6.5) affecting proftpd. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.5% (top 56%)
CISA exploited list	No
Weakness	CWE-126, CWE-190
Published	2026-07-20
Last modified	2026-07-30

Publisher (CNA): VulnCheck · Vendor: proftpd

Last updated 2026-07-30 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-20 15:16 UTCPublished CVE record published
2026-07-30 17:18 UTCUpdated Record last modified

proftpd proftpd UPGRADE

Affected: < 1.3.9c · 1.3.10 rc1 · 1.3.10 rc2

Fixed in: 1.3.9c

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy proftpd || rpm -q proftpd || proftpd --version

2. UPGRADE to 1.3.9c (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade proftpd

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade proftpd

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-63091?

proftpd: upgrade to 1.3.9c. Exact commands for each OS are on this page.

Is CVE-2026-63091 being exploited?

CVE-2026-63091 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-63091 affect?

CVE-2026-63091 affects proftpd. Severity is medium (CVSS 6.5). 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 UI

How urgent is CVE-2026-63091?

Priority 34/100. No elevated risk signals yet.

Software pages

ProFTPD vulnerabilities

Related CVEs

CVE-2026-35025 HIGH 8.1 UPGRADE ProFTPD through 1.3.9b and 1.3.10rc2 contains an access control bypass vulnerability that allows authenticated
CVE-2026-53994 HIGH 7.5 UPGRADE ProFTPD mod_sftp contains a heap-based buffer overflow reachable by an authenticated SFTP user
CVE-2015-3306 CRITICAL 10.0 EXPLOITED MITIGATE MITIGATE ProFTPD Improper Access Control Vulnerability
CVE-2026-63090 HIGH 8.8 UPGRADE ProFTPD before 1.3.9c and 1.3.10rc3 contains a heap-based buffer overflow vulnerability in the mod_sftp module

References

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