THREATPORT/VULNERABILITY/CVE-2026-42055
HIGH SEVERITY

CVE-2026-42055

Dos vulnerability

CVSS
8.1
EPSS
3.6%
EPSS pct
88th
Exploited
No known
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 vendor
F5
Affected product
Dos
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness type (CWE)
  • CWE-122 — Heap-based Buffer Overflow
  • CWE-787 — Out-of-bounds Write
  • CWE-131 — Incorrect Calculation of Buffer Size
Published
2026-06-17

Risk analysis

Based on its CVSS vector, this vulnerability is exploitable over the network, high attack complexity, requiring no privileges, no user interaction. Successful exploitation leads to high impact to confidentiality, high impact to integrity, high impact to availability.

Its EPSS score of 3.6% reflects a lower probability of exploitation activity in the wild over the next 30 days, placing it above 88% of all scored CVEs.

Check your external exposure to CVE-2026-42055

  • Confirm whether F5 Dos is running on any internet-facing host or subdomain.
  • Match discovered service fingerprints against the version affected by CVE-2026-42055.
  • Prioritise remediation if the asset is public, business-critical, or near authentication/payment flows.

How ThreatPort helps with CVE-2026-42055

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