[Snyk] Security upgrade next from 15.5.12 to 15.5.21

[peterj]

Snyk has created this PR to fix 2 vulnerabilities in the npm dependencies of this project.

Snyk changed the following file(s):

• package.json
• package-lock.json

Vulnerabilities that will be fixed with an upgrade:

	Issue	Score
	Server-side Request Forgery (SSRF) SNYK-JS-NEXT-18233136	701
	Server-side Request Forgery (SSRF) SNYK-JS-NEXT-18233752	701

Breaking Change Risk

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🦉 Server-side Request Forgery (SSRF)

[peterj]

This is a patch-level upgrade that moves from 15.5.12 to 15.5.21. According to the official Next.js announcements, version 15.5.21 is a security release that addresses multiple high and medium severity vulnerabilities.

As a patch release, it contains bug fixes and security patches and does not introduce any breaking API changes. An upgrade is highly recommended to ensure the application is secure.

Source: Next.js Blog

Notice 🤖: This content was augmented using artificial intelligence. AI-generated content may contain errors and should be reviewed for accuracy before use.

[kristin-kronstain-brown]

Closing: this is now addressed on the kkb-hugo-docs-migration branch (#406, commit 7adc835), which stays on the Next 15 line:

• next → ^15.5.21 (resolves 15.5.22)
• new overrides: postcss → ^8.5.23, sharp → ^0.35.0

All 24 Next.js advisories that applied to 15.5.12 are fixed as of 15.5.21, so the 15.x line is sufficient — npm audit now reports next, postcss, and sharp clean. Verified with npm ci and a full make build (Hugo docs + OpenNext worker); CI is green on #406.

For the record, this PR targeted the correct version. It is being closed because 15.5.22 has since been applied directly in #406, not because the change was wrong.