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Vulnerability · Published Dec 7, 2021 · Assigned by mitre

CVE-2021-42717

High 7.5

In plain English

A high-severity security flaw in the modsecurity package (Debian). There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 3.2% (higher than 88% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.

Severity (CVSS NVD)7.5High
Exploit odds (30 days)3.2%top 11.6% of all CVEs
Exploited in the wildNo reportsnot in CISA KEV
Attack tooling1Public PoC

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12modsecurity3.0.6-1DEBIAN-CVE-2021-42717
Debian:13modsecurity3.0.6-1DEBIAN-CVE-2021-42717
Debian:14modsecurity3.0.6-1DEBIAN-CVE-2021-42717
Debian:12modsecurity-apache2.9.5-1DEBIAN-CVE-2021-42717
Debian:13modsecurity-apache2.9.5-1DEBIAN-CVE-2021-42717
Debian:14modsecurity-apache2.9.5-1DEBIAN-CVE-2021-42717
Ubuntu:22.04:LTSmodsecurityno fix listedUBUNTU-CVE-2021-42717
Ubuntu:24.04:LTSmodsecurityno fix listedUBUNTU-CVE-2021-42717
Ubuntu:25.10modsecurityno fix listedUBUNTU-CVE-2021-42717
Ubuntu:26.04:LTSmodsecurityno fix listedUBUNTU-CVE-2021-42717
Ubuntu:26.10modsecurityno fix listedUBUNTU-CVE-2021-42717

Affected products (as reported)

VendorProductVersions
n/a n/a n/a

References