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Vulnerability record · CVE-2026-63091 · published 20 July 2026

CVE-2026-63091: Proftpd integer overflow vulnerability

PProftpd · Proftpd

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.

7.1 CVSS 4.0 High EPSS 0.53% · top 57.8% CWE-126 · CWE-126CWE-190 · Integer overflow
7.1CVSS 4.0 base score
0.53%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
6References
30 Jul 2026Last modified by NVD

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.

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/proftpd/proftpd/blob/master/RELEASE_NOTES Release Notes
https://github.com/proftpd/proftpd/commit/b9b7dde1bcd74bc23366484d53856b67b8d6d95e Patch
https://github.com/proftpd/proftpd/pull/2201 Issue TrackingPatch
https://github.com/proftpd/proftpd/releases/tag/v1.3.10rc3-3 ProductRelease Notes
https://github.com/proftpd/proftpd/releases/tag/v1.3.9c ProductRelease Notes
https://www.vulncheck.com/advisories/proftpd-mod-sftp-signed-integer-overflow-via-scp-size-record-parser PatchRelease NotesThird Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-63091), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.