Threat Intelligence / CVE / CVE-2026-42945

CVE-2026-42945 — F5 NGINX Plus

CVSS v3.1 8.1 (HIGH) · CVSS v4.0 9.2 · EPSS 0.8% (higher than 75.9% of all scored CVEs) · Priority 7.1/10 · Published 2026-05-13

As of 2026-05-21, CVE-2026-42945 is a HIGH-severity vulnerability in F5 NGINX Plus, CVSS v3.1 8.1, EPSS 0.8% (75.9th percentile). Threadlinqs Intelligence links 2 tracked threat campaigns to CVE-2026-42945, most recently “F5 Patches Multiple NGINX Vulnerabilities: Heap Overflow, Memory Disclosure, and Use-After-Free (CVE-2026-42533, CVE-2026-60005, CVE-2026-56434)”.

Last updated: 2026-05-21

What is CVE-2026-42945?

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_rewrite_module module. This vulnerability exists when the rewrite directive is followed by a rewrite, if, or set directive and an unnamed Perl-Compatible Regular Expression (PCRE) capture (for example, $1, $2) with a replacement string that includes a question mark (?). An unauthenticated attacker along with conditions beyond its 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. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

The record classifies CVE-2026-42945 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 122 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 75.9% of all scored CVEs
CISA KEV: Not listed in the CISA Known Exploited Vulnerabilities catalog
Threadlinqs priority: 7.1/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
Published: 2026-05-13, last modified 2026-05-21

Is CVE-2026-42945 being exploited?

It currently carries a trending score of 24 in the Threadlinqs vulnerability feed.

Affected products and versions

F5: NGINX Plus, NGINX Open Source

How to fix CVE-2026-42945

No vendor patch reference has been recorded for CVE-2026-42945 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-2026-42945

2 tracked threats in the Threadlinqs corpus reference CVE-2026-42945, either in the campaign’s CVE list or as an indicator on the campaign record.

F5 Patches Multiple NGINX Vulnerabilities: Heap Overflow, Memory Disclosure, and Use-After-Free (CVE-2026-42533, CVE-2026-60005, CVE-2026-56434) — CRITICAL · 2026-07-15
NGINX Rift — CVE-2026-42945 Heap Buffer Overflow in ngx_http_rewrite_module (CVSS v4 9.2 Critical, 18-Year-Old Pre-Auth RCE, Public PoC) — CRITICAL · 2026-05-14

Sources

Seeded from cveorg and not yet processed by the Threadlinqs enrichment pipeline, so blank CVSS, EPSS or KEV fields above mean NOT MEASURED rather than measured-absent.

my.f5.com

Full detection coverage & IOCs for threats exploiting CVE-2026-42945 are available via the Threadlinqs MCP server (Purple tier). View plans →

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