PT-2021-5748 · Unknown+5 · Modsecurity+5

Published 2021-11-22 · Updated 2025-07-03 · CVE-2021-42717

Positive Technologies (AI Summary)

CVSS v2.0

7.8

High

Base vector

AV:N/AC:L/Au:N/C:N/I:N/A:C

Name of the Vulnerable Software and Affected Versions ModSecurity versions 2.8.0 through 2.9.4 ModSecurity versions 3.0.0 through 3.0.5

Description The issue is related to the mishandling of excessively nested JSON objects, which can cause the web server to be unable to service legitimate requests. Crafted JSON objects with tens-of-thousands deep nesting can occupy one of the limited NGINX worker processes for minutes and consume almost all of the available CPU on the machine. Even moderately large HTTP requests, such as 300KB, can have this effect. This can be exploited by a remote attacker to perform a denial of service.

Recommendations For ModSecurity versions 2.8.0 through 2.9.4, consider disabling the handling of nested JSON objects until a patch is available. For ModSecurity versions 3.0.0 through 3.0.5, consider disabling the handling of nested JSON objects until a patch is available. As a temporary workaround, consider restricting the size of HTTP requests to minimize the risk of exploitation.

Exploit

Fix

Uncontrolled Recursion

Weakness Enumeration

CWE-674

Related Identifiers

ALT-PU-2021-3328

ALT-PU-2023-1799

AZL-44934

BDU:2022-00191

BIT-MODSECURITY-2021-42717

BIT-MODSECURITY2-2021-42717

CVE-2021-42717

DLA-3031-1

DSA-5023-1

MGASA-2021-0576

OESA-2021-1464

OESA-2022-1954

OPENSUSE-SU-2023:0257-1

OPENSUSE-SU-2023:0269-1

OPENSUSE-SU-2024:12118-1

USN-6370-1

Affected Products

Alt Linux

Debian

Linuxmint

Modsecurity

Nginx

Ubuntu

References · 45

• 🔥 https://trustwave.com/en-us/resources/blogs/spiderlabs-blog/modsecurity-dos-vulnerability-in-json-parsing-cve-2021-42717 · Exploit
• https://osv.dev/vulnerability/UBUNTU-CVE-2021-42717 · Vendor Advisory
• https://osv.dev/vulnerability/BIT-modsecurity-2021-42717 · Vendor Advisory
• https://cve.org/CVERecord?id=CVE-2021-42717 · Security Note
• https://osv.dev/vulnerability/OESA-2022-1954 · Vendor Advisory
• https://security-tracker.debian.org/tracker/CVE-2021-42717 · Vendor Advisory
• https://osv.dev/vulnerability/AZL-44934 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2021-42717 · Security Note
• https://osv.dev/vulnerability/DSA-5023-1 · Vendor Advisory
• https://bdu.fstec.ru/vul/2022-00191 · Security Note
• https://osv.dev/vulnerability/DLA-3031-1 · Vendor Advisory
• https://osv.dev/vulnerability/MGASA-2021-0576 · Vendor Advisory
• https://osv.dev/vulnerability/USN-6370-1 · Vendor Advisory
• https://osv.dev/vulnerability/CVE-2021-42717 · Vendor Advisory
• https://debian.org/security/2021/dsa-5023 · Vendor Advisory