HOME VULNERABILITIESCVE-2021-42717

HIGH

CVE-2021-42717

CWE-674Published: December 7, 2021· Updated: Jun 17, 2026

7.5

CVSS v3.1

Official Description

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.

Technical Analysis

CVE-2021-42717 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 7.5.

CVSS v3.1 Vector Breakdown

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges Req.None

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected Vendors & Products

Debian1 product(s)

debian linux

f51 product(s)

nginx modsecurity waf

Oracle2 product(s)

http serverzfs storage appliance kit

owasp1 product(s)

modsecurity

trustwave1 product(s)

modsecurity

Source: NVD CPE · 10 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time

Offensive Security exploit database

GitHub PoC Search

Community PoC repositories

Rapid7 / Metasploit

Metasploit module search

Security advisories & exploits

Official NIST entry

CVE Program entry

External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://www.oracle.com/security-alerts/cpuapr2022.html

PATCHhttps://www.oracle.com/security-alerts/cpuapr2022.html

ADVISORYhttps://lists.debian.org/debian-lts-announce/2022/05/msg00042.html

ADVISORYhttps://www.debian.org/security/2021/dsa-5023

ADVISORYhttps://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/modsecurity-dos-vulnerability-in-json-parsing-cve-2021-42717/

ADVISORYhttps://lists.debian.org/debian-lts-announce/2022/05/msg00042.html

ADVISORYhttps://www.debian.org/security/2021/dsa-5023

ADVISORYhttps://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/modsecurity-dos-vulnerability-in-json-parsing-cve-2021-42717/

All References (8)

→

https://lists.debian.org/debian-lts-announce/2022/05/msg00042.htmlMailing List · Third Party Advisory

→

https://www.debian.org/security/2021/dsa-5023Third Party Advisory

→

https://www.oracle.com/security-alerts/cpuapr2022.htmlPatch · Third Party Advisory

→

https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/modsecurity-dos-vulnerability-in-json-parsing-cve-2021-42717/Exploit · Mitigation · Vendor Advisory

→

https://lists.debian.org/debian-lts-announce/2022/05/msg00042.htmlMailing List · Third Party Advisory

→

https://www.debian.org/security/2021/dsa-5023Third Party Advisory

→

https://www.oracle.com/security-alerts/cpuapr2022.htmlPatch · Third Party Advisory

→

https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/modsecurity-dos-vulnerability-in-json-parsing-cve-2021-42717/Exploit · Mitigation · Vendor Advisory

Quick Facts

CVE IDCVE-2021-42717

CVSS Score7.5 / 10

SeverityHIGH

WeaknessCWE-674

CISA KEVNo

Affected5 vendor(s)

PublishedDec 7, 2021

Related CVEs (CWE-674)

CVE-2018-1000618

Recommended Actions

→Apply vendor patches immediately
→Monitor CVE-2021-42717 in threat intel feeds
→Review IDS/IPS signatures for exploitation attempts

Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.

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