CVE-2021-42717

Exp

ModSecurity 3.x through 3.0.5 mishandles excessively nested JSON objects. Crafted JSON objects with nesting tens-of-thousands deep could result in the web server being unable to service legitimate requests. Even a moderately large (e.g., 300KB) HTTP request can occupy one of the limited NGINX worker processes for minutes and consume almost all of the available CPU on the machine. Modsecurity 2 is similarly vulnerable: the affected versions include 2.8.0 through 2.9.4.

Published: 2021-12-07 Last update: 2025-07-03 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-42717 is rated High Exploit Risk (74.5/100): CVSS High severity, with medium exploitation likelihood (EPSS 2.04%). 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-2021-42717

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

Exploit prediction scoring system (EPSS) score for CVE-2021-42717

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 2025-11-29 1.71% 2.04% +0.34%
2 2025-11-21 5.28% 1.71% -3.57%
3 2025-11-18 — 5.28% —

Full EPSS history (29 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-42717

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-2021-42717

OS Trackers for CVE-2021-42717

vendor priority summary link
debian not yet assigned CVE-2021-42717 not yet assigned priority: Debian including 2 source packages (modsecurity, modsecurity-apache), 10 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 9, open 1. https://security-tracker.debian.org/tracker/CVE-2021-42717
suse high CVE-2021-42717 severity important: SUSE including 15 source package names (apache2-mod_security2, libmodsecurity3-3.0.10-bp154.2.3.1, …), 63 product×package rows across 44 product lines (HPE Helion OpenStack 8, SUSE CaaS Platform 4.0, … (44 product lines)): Known Not Affected 39, Fixed 24. https://www.suse.com/security/cve/CVE-2021-42717/
ubuntu medium CVE-2021-42717 medium priority: Ubuntu including 2 source packages (modsecurity, modsecurity-apache), 29 status rows across 15 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): ignored 12, not-affected 8, needs-triage 5, released 4. https://ubuntu.com/security/CVE-2021-42717

Affected software / configurations for CVE-2021-42717

Vendor Product Version Raw CPE
owasp modsecurity >= 3.0.0, < 3.0.6 cpe:2.3:a:owasp:modsecurity:*:*:*:*:*:*:*:*
trustwave modsecurity >= 2.0.0, < 2.9.5 cpe:2.3:a:trustwave:modsecurity:*:*:*:*:*:*:*:*
f5 nginx_modsecurity_waf r24 cpe:2.3:a:f5:nginx_modsecurity_waf:r24:*:*:*:*:*:*:*
f5 nginx_modsecurity_waf r25 cpe:2.3:a:f5:nginx_modsecurity_waf:r25:*:*:*:*:*:*:*
debian debian_linux 9.0 cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
debian debian_linux 11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
oracle http_server 12.2.1.3.0 cpe:2.3:a:oracle:http_server:12.2.1.3.0:*:*:*:*:*:*:*
oracle http_server 12.2.1.4.0 cpe:2.3:a:oracle:http_server:12.2.1.4.0:*:*:*:*:*:*:*
oracle zfs_storage_appliance_kit 8.8 cpe:2.3:a:oracle:zfs_storage_appliance_kit:8.8:*:*:*:*:*:*:*

References for CVE-2021-42717

cvelogic Threat Intelligence