ProFTPD up to 1.3.9b/1.3.10rc2 Mod Sftp integer overflow

Summaryinfo

A vulnerability, which was classified as very critical, was found in ProFTPD up to 1.3.9b/1.3.10rc2. This impacts an unknown function of the component Mod Sftp. Executing a manipulation can lead to integer overflow. This vulnerability is registered as CVE-2026-63091. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability classified as very critical was found in ProFTPD up to 1.3.9b/1.3.10rc2. This vulnerability affects some unknown functionality of the component Mod Sftp. The manipulation with an unknown input leads to a integer overflow vulnerability. The CWE definition for the vulnerability is CWE-190. The product performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-63091 since 07/15/2026. The exploitation appears to be easy. The attack can be initiated remotely. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 07/20/2026).

Upgrading to version 1.3.9c or 1.3.10rc3 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-45961). Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• File Transfer Software

Name

• ProFTPD

Version

• 1.3.9a
• 1.3.9b
• 1.3.10rc1
• 1.3.10rc2

License

• open-source

Website

• Product: https://github.com/proftpd/proftpd/

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Once again VulDB remains the best source for vulnerability data.

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