ProFTPD mod_sftp Heap Buffer Overflow via Unsigned Integer Underflow and Size Truncation

Description

ProFTPD mod_sftp contains a heap-based buffer overflow reachable by an authenticated SFTP user. The fxp_packet_read() function accepts the attacker-supplied 32-bit big-endian SFTP packet length without a minimum sanity check. A value of 0 causes an unsigned subtraction elsewhere in the read path to underflow to approximately 4 GB. That oversized request reaches the core memory allocator, where the rounded size is computed in size_t but passed to new_block() as a 32-bit int; the low 32 bits of 0x100000000 are 0, so new_block() returns a small (~512-byte) block while the caller is told it received ~4 GB. The subsequent fill loop then streams attacker-controlled bytes past the end of the 544-byte allocation, producing an attacker-controlled heap buffer overflow. An authenticated user can crash the per-connection ProFTPD session child on demand with a single malformed SFTP packet (packet_len=0 followed by a body greater than approximately 544 bytes), producing reliable authenticated remote denial of service. Depending on heap layout and adjacent allocations, heap metadata corruption and further consequences beyond denial of service may be possible, though only denial of service is demonstrated by the supplied proof of concept.

Scores

EPSS (exploitation in 30 days)

0.45% · top 61% of all CVEs (6 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: total

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.7.

Weakness

• CWE-122: Heap-based Buffer Overflow (opens in a new tab)All about CWE-122 and its CVEs

Affected products

• ProFTPD Project · ProFTPD

  • affected < 1.3.10

References (3)

• Product (opens in a new tab)product
• Patch Commit (opens in a new tab)patch
• https://www.vulncheck.com/advisories/proftpd-mod-sftp-heap-buffer-overflow-via-unsigned-integer-underflow-and-size-truncation (opens in a new tab)third-party-advisory

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-53994](https://trackcve.app/badge/CVE-2026-53994.svg)](https://trackcve.app/cve/CVE-2026-53994)

Record last updated 28 Jul 2026, 01:49 UTC.