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NGINX CVE-2026-42533

| EUVDEUVD-2026-44683 CRITICAL
Heap-based Buffer Overflow (CWE-122)
2026-07-15 f5 GHSA-fxfg-v4rj-hp95
9.2
CVSS 4.0 · Vendor: f5
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Severity by source

Vendor (f5) PRIMARY
9.2 HIGH
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/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
vuln.today AI
8.1 HIGH

Network-reachable and unauthenticated (AV:N/PR:N/UI:N); AC:H because success depends on a specific config pattern plus ASLR disabled/bypassed for the C:H/I:H code-execution path, with A:H from worker crashes.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
4.0 AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
SUSE
8.1 HIGH
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Red Hat
7.0 HIGH
qualitative

Primary rating from Vendor (f5).

CVSS VectorVendor: f5

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

5
Re-analysis Queued
Jul 15, 2026 - 15:22 vuln.today
cvss_changed
Severity Changed
Jul 15, 2026 - 15:22 NVD
HIGH CRITICAL
CVSS changed
Jul 15, 2026 - 15:22 NVD
8.1 (HIGH) 9.2 (CRITICAL)
Analysis Generated
Jul 15, 2026 - 15:22 vuln.today
CVE Published
Jul 15, 2026 - 14:33 cve.org
CRITICAL 9.2

DescriptionCVE.org

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.

AnalysisAI

Heap buffer overflow in NGINX Plus and NGINX Open Source lets unauthenticated remote attackers crash worker processes (DoS) and, on hosts with ASLR disabled or bypassed, potentially execute arbitrary code by sending crafted HTTP requests. The flaw is a data-plane-only issue triggered when a regex-based map directive references the map's regex capture variables before the map output variable in a string expression, or via a non-cacheable variable under certain conditions. F5 has released a patched version; no public exploit identified at time of analysis and it is not listed in CISA KEV.

Technical ContextAI

The vulnerability lives in NGINX's variable-evaluation machinery for the map module, a core configuration construct that maps one variable to another and supports PCRE-style regex matching with numbered capture groups. When a string expression evaluates the map's regex capture variables ($1, $2, etc.) before evaluating the map output variable, or when a non-cacheable variable is used under specific conditions, NGINX mismanages the heap allocation sizing/ordering for the resulting string, producing a heap-based buffer overflow (CWE-122: Heap-based Buffer Overflow) in the worker process. Affected products per CPE are cpe:2.3:a:f5:nginx_plus and cpe:2.3:a:f5:nginx_open_source, spanning both the commercial NGINX Plus and the open-source NGINX web server/reverse proxy. Because the fault is in HTTP request processing on the data plane, the NGINX control/management plane is not exposed.

RemediationAI

Patch available per vendor advisory - upgrade to the fixed NGINX Plus and/or NGINX Open Source release published by F5; the exact fixed version is not stated in the provided data, so verify the target version directly in the F5 advisory at https://my.f5.com/manage/s/article/K000162097 before deploying. As an immediate compensating control until patching, audit your nginx.conf for the vulnerable pattern: any map directive using regex matching where a string expression references the map's regex capture variables ($1, $2, …) before referencing the map output variable, and reorder the expression so the map output variable is evaluated first; also review string expressions that use non-cacheable variables in that context. Reordering these expressions removes the trigger with minimal functional side effect, though it requires per-config validation and reload testing. Ensure ASLR remains enabled at the OS level (e.g. kernel.randomize_va_space=2 on Linux) so that any residual overflow is limited to a worker restart (DoS) rather than code execution - this does not fix the bug but materially reduces impact. Because this is a data-plane issue with no control-plane exposure, restricting or rate-limiting untrusted HTTP request sources at an upstream WAF/load balancer can reduce exposure but will not fully prevent triggering.

CVE-2023-44487 HIGH POC
7.5 Oct 10

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9.2 May 13

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9.2 Jun 17

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CVE-2026-56434 HIGH
8.3 Jul 15

Heap buffer over-read in the ngx_http_ssi_module of NGINX Open Source and NGINX Plus lets an unauthenticated man-in-the-

CVE-2026-42946 HIGH
8.3 May 13

Memory disclosure and denial-of-service in NGINX's SCGI and uWSGI proxy modules allow attackers with man-in-the-middle p

CVE-2024-24990 HIGH
7.5 Feb 14

When NGINX Plus or NGINX OSS are configured to use the HTTP/3 QUIC module, undisclosed requests can cause NGINX worker p

Vendor StatusVendor

SUSE

Severity: Important
Product Status
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Server Applications 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected
SUSE Linux Enterprise Server 16.1 Affected

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CVE-2026-42533 vulnerability details – vuln.today

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