CVE-2026-42554

Fiber is a web framework for Go. Prior to 2.52.12 and 3.1.0, Cross-Site Scripting vulnerability in Go Fiber allows a remote attacker to inject arbitrary HTML/JavaScript by supplying Accept: text/html on any request whose handler passes attacker-influenced data to the AutoFormat() feature. The developer opts into content negotiation by calling AutoFormat(), but does not opt into raw HTML emission for a particular request; Fiber chooses that branch from attacker-controlled Accept. The html branch is the sole outlier in a method whose name (AutoFormat) and symmetrical structure actively telegraph "safe, format-agnostic reply." This vulnerability is fixed in 2.52.12 and 3.1.0.

Affected products

Fiber

Gofiber Fiber

< 2.52.12, 3.1.0

Fix

Available

CVSS 3.1

6.1 MEDIUM

EPSS

0.2% (12th percentile)

Weakness

CWE-79

NVD status

Analyzed

Published

2026-05-11

No exploit for CVE-2026-42554 has been indexed yet. Our index is built from live traffic and upstream syncs, so this page can only say what it knows — not that no exploit exists.