ASLR bypass via unchecked SCP size conversion
Published Jul 20, 2026 · Updated Jul 20, 2026
Buffer over-read in ProFTPD before 1.3.9c and 1.3.10rc1 through 1.3.10rc2 allows remote authenticated users to disclose process memory. The recv_filesz function in contrib/mod_sftp/scp.c accumulates the client size string into off_t without a range check, so UINT64_MAX becomes negative and later converts to an approximately 4 GB read length. Any low-privilege SFTP account with SCP upload access can recover libc, libcrypto, and PIE pointers that defeat ASLR for same-process exploit chains.
Summary
What happened
Buffer over-read in ProFTPD before 1.3.9c and 1.3.10rc1 through 1.3.10rc2 allows remote authenticated users to disclose process memory. The recv_filesz function in contrib/mod_sftp/scp.c accumulates the client size string into off_t without a range check, so UINT64_MAX becomes negative and later converts to an approximately 4 GB read length. Any low-privilege SFTP account with SCP upload access can recover libc, libcrypto, and PIE pointers that defeat ASLR for same-process exploit chains.
The record
- CVE
- CVE-2026-63091
- Published
- Jul 20, 2026
- Updated
- Jul 20, 2026
- Vendor
- ProFTPD Project
- Product
- ProFTPD
- Classifications
- CWE-126, CWE-190, T1190
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Jul 20, 2026CVE publishedPublication date reported by the CVE source.
- Jul 20, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <1.3.9c
- Affected versionversion=1.3.10rc1 <1.3.10rc3
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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