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.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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.
Which versions are affected by CVE-2026-63091?
It affects 1 product.
Products include 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
Sources
Also known as DEBIAN-CVE-2026-63091, GHSA-gqm5-f386-9r92, UBUNTU-CVE-2026-63091.