Highly exploitable, CVE-2026-53994 poses a critical security risk that could lead to severe breaches.
Status: Received on 18 Jul 2026, 20:17 UTC
Published on: 18 Jul 2026, 20:17 UTC
CVSS Release: version 3
disclosure@vulncheck.com
Primary
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
CVE-2026-53994: 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.
The exploitability of CVE-2026-53994 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).
This vulnerability, CVE-2026-53994, requires a high level of attack complexity and low privileges, making it difficult but not impossible to exploit. Organizations should ensure robust security configurations to mitigate risks.
A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.
Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.
Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.
Above is the CVSS Sub-score Breakdown for CVE-2026-53994, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.
Below is the Impact Analysis for CVE-2026-53994, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.
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