CVE-2021-47865
Published: 21 January 2026
Summary
CVE-2021-47865 is a high-severity Allocation of Resources Without Limits or Throttling (CWE-770) vulnerability in Proftpd (inferred from references). Its CVSS base score is 7.5 (High).
Operationally, ranked at the 5.7th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
Threat & Defense Details
Likely Mitigating ControlsAI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
This control implements explicit throttling on session allocation, addressing the weakness of allocating resources without limits.
Plan testing exercises resource allocation limits and throttling during simulated failures, directly addressing weaknesses that allow unbounded resource use.
Contingency plan updates ensure recovery strategies address unbounded resource allocation, making it harder for attackers to exploit lack of throttling to cause prolonged outages.
Provides continuity when unbounded resource allocation at the primary site leads to exhaustion and downtime.
Alternate services allow operations to continue when primary allocation of resources lacks limits or throttling.
Explicit planning of security-related actions requires defining limits, windows, and resource allocations, making allocation without throttling far less likely.
Measures of performance include tracking allocation behavior and throttling effectiveness, reducing the window for resource exhaustion attacks.
Imposes an inactivity-based limit on network resource allocation, throttling the number of concurrently held connections.
NVD Description
ProFTPD 1.3.7a contains a denial of service vulnerability that allows attackers to overwhelm the server by creating multiple simultaneous FTP connections. Attackers can repeatedly establish connections using threading to exhaust server connection limits and block legitimate user access.
Deeper analysisAI
CVE-2021-47865 is a denial of service vulnerability affecting ProFTPD version 1.3.7a. The flaw enables attackers to overwhelm the server by creating multiple simultaneous FTP connections, leveraging threading to exhaust server connection limits and block legitimate user access. It carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) and maps to CWE-770 (Allocation of Resources Without Limits or Throttling).
The vulnerability can be exploited by any remote attacker requiring no privileges, authentication, or user interaction, with low attack complexity over the network. Successful exploitation results in resource exhaustion, rendering the FTP server unavailable to legitimate users by maxing out connection slots.
Advisories and related resources include the Vulncheck advisory at https://www.vulncheck.com/advisories/proftpd-a-remote-denial-of-service, a ProFTPD GitHub issue at https://github.com/proftpd/proftpd/issues/1298, and the official ProFTPD site at http://www.proftpd.org/. A proof-of-concept exploit is publicly available at https://www.exploit-db.com/exploits/49697.
Details
- CWE(s)