NGINX
CVE-2026-42055
CRITICAL
Severity by source
CVSS:4.0/AV:N/AC:H/AT:P/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
Network-reachable and unauthenticated (AV:N/PR:N/UI:N), but AC:H because exploitation requires a non-default three-setting config and ASLR bypass for full C/I/A impact.
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Primary rating from Vendor (f5).
CVSS VectorVendor: f5
CVSS:4.0/AV:N/AC:H/AT:P/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
Lifecycle Timeline
7DescriptionCVE.org
NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_proxy_v2_module and ngx_http_grpc_module modules. This vulnerability exists when the proxy_http_version to 2 or grpc_pass directives are used to proxy HTTP/2 traffic, the ignore_invalid_headers directive is set to off, and the large_client_header_buffers directive size is larger than 2 megabytes. A remote, unauthenticated attacker, along with conditions beyond their control, could send large headers while creating an upstream request. This may cause a heap-based 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.
Articles & Coverage 2
AnalysisAI
Heap-based buffer overflow in NGINX Plus and NGINX Open Source affects deployments that proxy HTTP/2 or gRPC traffic upstream when ignore_invalid_headers is off and large_client_header_buffers exceeds 2 MB. Remote unauthenticated attackers sending oversized headers can crash the worker process, and where ASLR is disabled or bypassable, achieve arbitrary code execution. No public exploit identified at time of analysis and CISA SSVC marks exploitation as 'none', but technical impact is rated total.
Technical ContextAI
The flaw lives in ngx_http_proxy_v2_module and ngx_http_grpc_module - the upstream HTTP/2 and gRPC proxy paths in NGINX. When proxy_http_version is set to 2 or grpc_pass is used, NGINX re-encodes downstream headers into HPACK frames for the upstream connection. With large_client_header_buffers configured above 2 MB and ignore_invalid_headers set to off, the header-handling path mismanages the buffer boundary, producing a CWE-122 heap-based buffer overflow in the worker. The affected CPEs cover both f5:nginx_open_source and f5:nginx_plus across all versions still under technical support, indicating the bug exists in the shared upstream codebase rather than a Plus-only module.
RemediationAI
Patch available per vendor advisory - upgrade NGINX Open Source or NGINX Plus to the fixed branch listed in F5 article K000161584 (https://my.f5.com/manage/s/article/K000161584); exact fix versions were not included in the input data and should be read directly from that advisory. If immediate upgrade is not possible, remove the vulnerable configuration combination by lowering large_client_header_buffers to 2 MB or less (default is 8k, so most operators only need to revert custom tuning), or by setting ignore_invalid_headers back to its default of on, or by switching proxy_http_version back to 1.1 where the upstream service supports it (note: this disables HTTP/2 multiplexing to that backend and is not viable for grpc_pass blocks). Ensure ASLR is enabled on the host as defense-in-depth so that successful overflows degrade to a worker restart rather than RCE.
More in Nginx Open Source
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Heap buffer overflow in NGINX Plus and NGINX Open Source ngx_http_rewrite_module can be triggered by unauthenticated rem
Heap buffer overflow in NGINX Plus and NGINX Open Source lets unauthenticated remote attackers crash worker processes (D
Limited memory disclosure and worker-process restart in NGINX Plus and NGINX Open Source arise when the optional ngx_htt
Buffer overflow in NGINX's DAV module allows remote attackers to crash worker processes or manipulate file names outside
NGINX worker process crashes via null pointer dereference in the mail authentication module when CRAM-MD5 or APOP authen
Integer overflow in NGINX 32-bit builds with the ngx_http_mp4_module allows local attackers to corrupt or overwrite work
NGINX Open Source and NGINX Plus contain a buffer over-read or over-write vulnerability in the ngx_http_mp4_module that
Heap buffer over-read in the ngx_http_ssi_module of NGINX Open Source and NGINX Plus lets an unauthenticated man-in-the-
Memory disclosure and denial-of-service in NGINX's SCGI and uWSGI proxy modules allow attackers with man-in-the-middle p
When NGINX Plus or NGINX OSS are configured to use the HTTP/3 QUIC module, undisclosed requests can cause NGINX worker p
Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Heap Overflow
View allVendor 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 16.0 | Affected |
| SUSE Linux Enterprise Server 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP7 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.0 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| openSUSE Leap 16.0 | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP4 | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP5 | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP4 | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP5 | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP6 | Affected |
| SUSE Linux Enterprise Server 15 SP4 | Affected |
| SUSE Linux Enterprise Server 15 SP4-LTSS | Affected |
| SUSE Linux Enterprise Server 15 SP5 | Affected |
| SUSE Linux Enterprise Server 15 SP5-LTSS | Affected |
| SUSE Linux Enterprise Server 15 SP6 | Affected |
| SUSE Linux Enterprise Server 15 SP6-LTSS | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP6 | Affected |
| SUSE Manager Proxy 4.3 | Affected |
| SUSE Manager Proxy LTS 4.3 | Affected |
| SUSE Manager Retail Branch Server 4.3 | Affected |
| SUSE Manager Retail Branch Server LTS 4.3 | Affected |
| SUSE Manager Server 4.3 | Affected |
| SUSE Manager Server LTS 4.3 | Affected |
| SUSE CaaS Platform 4.0 | Affected |
| SUSE Enterprise Storage 6 | Affected |
| SUSE Enterprise Storage 7 | Affected |
| SUSE Enterprise Storage 7.1 | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP1 | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP1-ESPOS | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP1-LTSS | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP2 | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP2-ESPOS | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP3 | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP3-ESPOS | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS | Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP6 | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP1 | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP2 | Affected |
| SUSE Linux Enterprise Module for Server Applications 15 SP3 | Affected |
| SUSE Linux Enterprise Real Time 15 SP2 | Affected |
| SUSE Linux Enterprise Real Time 15 SP3 | Affected |
| SUSE Linux Enterprise Real Time 15 SP4 | Affected |
| SUSE Linux Enterprise Server 15 SP1 | Affected |
| SUSE Linux Enterprise Server 15 SP1-BCL | Affected |
| SUSE Linux Enterprise Server 15 SP1-LTSS | Affected |
| SUSE Linux Enterprise Server 15 SP2 | Affected |
| SUSE Linux Enterprise Server 15 SP2-BCL | Affected |
| SUSE Linux Enterprise Server 15 SP2-LTSS | Affected |
| SUSE Linux Enterprise Server 15 SP3 | Affected |
| SUSE Linux Enterprise Server 15 SP3-BCL | Affected |
| SUSE Linux Enterprise Server 15 SP3-LTSS | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP1 | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP2 | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP3 | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP4 | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP5 | Affected |
| SUSE Manager Proxy 4.0 | Affected |
| SUSE Manager Proxy 4.1 | Affected |
| SUSE Manager Proxy 4.2 | Affected |
| SUSE Manager Retail Branch Server 4.0 | Affected |
| SUSE Manager Retail Branch Server 4.1 | Affected |
| SUSE Manager Retail Branch Server 4.2 | Affected |
| SUSE Manager Server 4.0 | Affected |
| SUSE Manager Server 4.1 | Affected |
| SUSE Manager Server 4.2 | Affected |
| openSUSE Leap 15.3 | Affected |
| openSUSE Leap 15.4 | Affected |
| openSUSE Leap 15.5 | Affected |
| openSUSE Leap 15.6 | Affected |
| private-registry/1.2/harbor-portal private-registry/harbor-nginx private-registry/harbor-portal suse/nginx suse/rmt-nginx | Affected |
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