CVE-2021-40524

Exp

In Pure-FTPd before 1.0.50, an incorrect max_filesize quota mechanism in the server allows attackers to upload files of unbounded size, which may lead to denial of service or a server hang. This occurs because a certain greater-than-zero test does not anticipate an initial -1 value. (Versions 1.0.23 through 1.0.49 are affected.)

Published: 2021-09-05 Last update: 2025-11-04 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-40524 is rated High Exploit Risk (78.3/100): CVSS High severity, with high exploitation likelihood (EPSS 30.19%, 97th percentile). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-40524

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-40524

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-02 30.70% 30.19% -0.51%
2 2026-03-05 24.04% 30.70% +6.67%
3 2025-12-29 — 24.04% —

Full EPSS history (20 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-40524

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-40524

OS Trackers for CVE-2021-40524

vendor priority summary link
alpine — CVE-2021-40524: 1 source package rows (pure-ftpd); 2 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 2. https://security.alpinelinux.org/vuln/CVE-2021-40524
debian not yet assigned CVE-2021-40524 not yet assigned priority: Debian including 1 source packages (pure-ftpd), 4 status rows across 4 suites (bookworm, bullseye, sid, trixie): resolved 4. https://security-tracker.debian.org/tracker/CVE-2021-40524
suse high CVE-2021-40524 severity important: SUSE including 2 source package names (pure-ftpd-1.0.43-30.11.1, pure-ftpd-1.0.50-1.1), 2 product×package rows across 2 product lines (SUSE Linux Enterprise Server 11 SP3-TERADATA, openSUSE Tumbleweed): Fixed 2. https://www.suse.com/security/cve/CVE-2021-40524/
ubuntu low CVE-2021-40524 low priority: Ubuntu including 1 source packages (pure-ftpd), 15 status rows across 15 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): ignored 7, needs-triage 7, DNE 1. https://ubuntu.com/security/CVE-2021-40524

Affected software / configurations for CVE-2021-40524

Vendor Product Version Raw CPE
pureftpd pure-ftpd >= 1.0.23, < 1.0.50 cpe:2.3:a:pureftpd:pure-ftpd:*:*:*:*:*:*:*:*

References for CVE-2021-40524

cvelogic Threat Intelligence