Buffer overflow in F5 Dos
CVE-2026-42055
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.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.065 (93.8th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 94th percentile — 93.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.065 · newest: 0.065 · change: 0.000
Affected products
- F5 Dos — versions 4.9.0
- F5 nginx App Protect Dos
- F5 nginx App Protect Waf
- F5 nginx Gateway Fabric
- F5 nginx Ingress Controller — versions 4.0.0, 4.0.1
- F5 nginx Instance Manager
- F5 nginx Open Source — versions 1.13.10, 1.30.2
- F5 nginx Open Source — versions 1.31.1
- F5 nginx Plus — versions 37.0, R36
- F5 nginx Plus — versions r3, r30, r31
Weakness classification (CWE)
Public proof-of-concept exploits
References
- my.f5.com/manage/s/article/K000161584 (vendor-advisory, Vendor Advisory)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c (Third Party Advisory)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c (Third Party Advisory)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c (Third Party Advisory, Issue Tracking)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c (Third Party Advisory)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c (Third Party Advisory)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c (Third Party Advisory)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c (Third Party Advisory)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c (Third Party Advisory)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c (Third Party Advisory)
Frequently asked questions
- What is CVE-2026-42055?
- CVE-2026-42055 is a high-severity vulnerability in F5 Dos, classified under Heap-based Buffer Overflow. CVSS score: 8.1/10. Published 2026-06-17.
- How severe is CVE-2026-42055?
- High severity. CVSS v3 base score is 8.1 out of 10.
- Is CVE-2026-42055 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.