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.
The record classifies CVE-2026-42533 under weakness class CWE-122. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on confidentiality, integrity, availability. 2 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 104 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 8.1 — HIGH
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H - CVSS v4.0 base score
- 9.2
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N - EPSS (FIRST)
- 0.8% probability of exploitation in the next 30 days, higher than 58.2% of all scored CVEs
- CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 8.4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-07-15, last modified 2026-07-29
Is CVE-2026-42533 being exploited?
Weaponised exploit code for CVE-2026-42533 is publicly available. 10 public proof-of-concept repositories are tracked for this identifier. It currently carries a trending score of 36 in the Threadlinqs vulnerability feed.
- imbas007/CVE-2026-42533 (github)
- 0xCyberstan/CVE-2026-42533-Config-Scanner (github)
- Daniyal48/ghostlock-vagrant-box (github)
- seguridadentrerios/CVE-2026-42533 (github)
- 0xCyberstan/CVE-2026-42533-POC (github)
- srkyn/nginx-map-risk-audit (github)
- suominen/CVE-2026-42533 (github)
- gagaltotal/CVE-2026-42533-nginx (github)
Affected products and versions
- F5: NGINX Plus, NGINX Open Source
How to fix CVE-2026-42533
No vendor patch reference has been recorded for CVE-2026-42533 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.
Threat activity tracking CVE-2026-42533
1 tracked threat in the Threadlinqs corpus references CVE-2026-42533, either in the campaign’s CVE list or as an indicator on the campaign record.
Sources
Enriched from CVE.org, FIRST EPSS, public proof-of-concept repositories. Last verified by Threadlinqs on .