CVE-2026-58404: Hugo security.http.urls deny rules bypassed by alternate IPv4 encodings

Severity: medium (CVSS 6.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-06 · updated 2026-10-25
Weakness: CWE-918

Description

Hugo is a static site generator. From v0.162.0 through v0.163.0, the default security.http.urls policy denies requests to loopback, internal, and cloud-metadata IPv4 literals, but the deny rule only matched dotted-decimal notation, so alternate IPv4 encodings of the same addresses, including integer, hex, or octal, passed the policy. When a template passes an untrusted or data-derived URL to resources.GetRemote and the host platform uses the cgo system resolver, these encodings resolve to the blocked address, allowing build-time server-side requests to loopback and internal services, including the cloud-metadata endpoint in hosted or CI builds; the same check is reused on redirects, so the gap also applies to each redirect hop. This issue is fixed in v0.163.1.

Affected products

gohugoio hugo: from 0.162.0 before 0.163.1 — fixed in 0.163.1

How to fix

Upgrade to a fixed version: gohugoio hugo 0.163.1. Check the vendor advisory for mitigations.

References

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