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HIGH

CVE-2026-42533

NGINX Map directive and Regex matching vulnerability

CVSS v3

8.1

HIGH

EPSS Score

0.9 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

none

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • nginxBitnamifrom 0.9.6 · fixed in 1.30.4and 1 other package
  • nginxAlmaLinux:10all versions · fixed in 2:1.26.3-6.el10_2.7and 9 other packages
  • nginxAlmaLinux:9all versions · fixed in 2:1.26.3-9.module_el9.8.0+309+b8a3c30d.4and 9 other packages
  • nginxAlmaLinux:8all versions · fixed in 1:1.24.0-3.module_el8.10.0+4275+5756017d.5.alma.1and 8 other packages

Vendor advisories

  • CVE-2026-42533 Red Hat Product Security417 products fixed · 1 known affected

    nginx: NGINX: Arbitrary code execution via crafted HTTP requests

    insights-proxy/insights-proxy-container-rhel9 as a component of Red Hat Lightspeed proxy 1

  • RHSA-2026:79357 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Red Hat Cost Management On-Premise container image update

  • RHSA-2026:67308 Red Hat Product Security67 products fixed

    Red Hat Security Advisory: nginx:1.24 security update

  • RHSA-2026:67314 Red Hat Product Security99 products fixed

    Red Hat Security Advisory: nginx security update

  • RHSA-2026:67315 Red Hat Product Security59 products fixed

    Red Hat Security Advisory: nginx:1.24 security update

  • RHSA-2026:67283 Red Hat Product Security67 products fixed

    Red Hat Security Advisory: nginx:1.26 security update

2 more advisories

Full record on NVD

Description

A vulnerability exists in NGINX Plus and NGINX Open Source when a map directive uses regex matching and a string expression references the map's regex capture variables before referencing the map output variable. Alternatively, the same result could be achieved by using a non-cacheable variable in a string expression under certain conditions. An unauthenticated attacker along with conditions beyond their control can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow in the NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. Impact: This vulnerability may allow remote attackers to cause a denial-of-service (DoS) on the NGINX system or to possibly trigger a code execution. There is no control plane exposure; this is a data plane issue only.  Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Published
2026-07-15
Last Modified
2026-07-16

Frequently asked questions

What is CVE-2026-42533?

A vulnerability exists in NGINX Plus and NGINX Open Source when a map directive uses regex matching and a string expression references the map's regex capture variables before referencing the map output variable. Alternatively, the same result could be achieved by using a non-cacheable variable in a string expression under certain conditions. An unauthenticated attacker along with conditions beyond their control can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow in the NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. Impact: This vulnerability may allow remote attackers to cause a denial-of-service (DoS) on the NGINX system or to possibly trigger a code execution. There is no control plane exposure; this is a data plane issue only.  Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Is CVE-2026-42533 actively exploited?

Active exploitation of CVE-2026-42533 has not been confirmed. Its EPSS score was 0.9% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-42533?

CVE-2026-42533 has a CVSS v3 base score of 8.1 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.

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