CVE-2026-42554: Gofiber Fiber

Medium severity, CVSS 6.1. EPSS: 0.3% chance of exploitation in the next 30 days.

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

• Gofiber Fiber: before 2.52.12 (fixed in 2.52.12); from 3.0.0, before 3.1.0 (fixed in 3.1.0)

Published 2026-05-11. Last modified 2026-06-17.