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CVE-2026-42533

NGINX Map directive and Regex matching vulnerability

Critical9.2Public exploitEPSS 6.3%
Published
Updated
Reserved
Assigned by
f5

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.

Public exploit

An exploit or proof of concept is public: anyone can try it against an unpatched system. CISA's SSVC rates its exploitation: a proof of concept is public.

Timeline

  1. ID reserved

    By f5

  2. · 2 months later

    Published

  3. · 4 months later

    Record updated

Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.

Scores

CVSS scores of CVE-2026-42533, by who scored it
Scored byCVSSScoreVector
f5CNA (assigner)4.0Critical9.2CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
f5CNA (assigner)3.1High8.1CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
NVDNVD · Analyzed4.0Critical9.2CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS (exploitation in 30 days)
6.3% · top 6.4% of all CVEs (7 Nov 2026)
CISA SSVC
Exploitation: poc · Automatable: no · Technical impact: total
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.2.

Weakness

Affected products

  • F5 · NGINX Plus

    • affected 37.0.0.1 – < 37.0.3.1
    • affected R36 – < R36 P7
    • affected R33 – < *

  • F5 · NGINX Open Source

    • affected 1.31.2 – < 1.31.3
    • affected 0.9.6 – < 1.30.4

References (1)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .