medium6.1
CVE-2026-42554
Fiber vulnerable to XSS in AutoFormat Content Negotiation
Impact
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 packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| go | github.com/gofiber/fiber/v3 | <= 3.1.0 | 3.2.0 |
| go | github.com/gofiber/fiber/v2 | <= 2.52.12 | 2.52.13 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Gofiber | Fiber | before 2.52.12 from 3.0.0 before 3.1.0 |