Cyber Resilience

CVE-2021-42717

HighPublic PoCDDoS

Published: 07 December 2021

Published
07 December 2021
Modified
03 July 2025
KEV Added
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Patch
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CVSS Score v3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS Score 0.0204 84.2th percentile
Risk Priority 16 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2021-42717 is a high-severity Uncontrolled Recursion (CWE-674) vulnerability in Debian Debian Linux. Its CVSS base score is 7.5 (High).

Operationally, ranked in the top 15.8% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

EU & UK References

Vulnerability details

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…

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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.

CWE(s)
CWE-674

Related Threats

No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.

Affected Assets

owasp
modsecurity
3.0.0 — 3.0.6
trustwave
modsecurity
2.0.0 — 2.9.5
f5
nginx modsecurity waf
r24, r25
debian
debian linux
10.0, 11.0, 9.0
oracle
http server
12.2.1.3.0, 12.2.1.4.0
oracle
zfs storage appliance kit
8.8

Mitigating Controls

Likely Mitigating Controls AI

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.

CP-7 Alternate Processing Site
addresses: CWE-674

Supports resumption at alternate site when uncontrolled recursion causes primary site failure or crash.

SC-5 Denial-of-service Protection
addresses: CWE-674

Prevents uncontrolled recursion that exhausts stack or CPU resources.

References