# CVE-2026-42055

## Summary

- **CVE ID:** CVE-2026-42055
- **Severity:** CRITICAL
- **CVSS Score:** 9.2 (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)
- **CWE:** CWE-122
- **Published:** Jun 17, 2026
- **Last Modified:** Sep 14, 2026

## Description

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.

## Affected Products

- F5 — NGINX Open Source (1.13.10)
- F5 — NGINX Open Source (1.30.2)
- F5 — NGINX Plus (37.0)
- F5 — NGINX Plus (R36)

## References

- [CNA](https://my.f5.com/manage/s/article/K000161584)
- [redhat-SADP](https://access.redhat.com/security/cve/CVE-2026-42055)
- [redhat-SADP](https://bugzilla.redhat.com/show_bug.cgi?id=2489866)
- [redhat-SADP](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42055.json)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:27197)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:36364)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:36618)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:36331)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:36639)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:38847)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:44481)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:46836)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:58981)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 6.54%
- **EPSS Percentile:** 93.5

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._