Vulnerability · Published May 11, 2026 · Assigned by GitHub_M

CVE-2026-42554Fiber: XSS in AutoFormat Content Negotiation

Medium 5.3

In plain English

A medium-severity cross-site scripting in fiber from gofiber. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 12% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)5.3Medium

Exploit odds (30 days)0.2%top 88.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/gofiber/fiber/v2	2.52.13	GO-2026-5585
Go	github.com/gofiber/fiber/v2	2.52.13	GHSA-qjv7-627w-8qjv
Go	github.com/gofiber/fiber/v3	3.2.0	GO-2026-5585
Go	github.com/gofiber/fiber/v3	3.2.0	GHSA-qjv7-627w-8qjv

Affected products (as reported)

Vendor	Product	Versions
gofiber	fiber	< 2.52.13>= 3.0.0-beta.2, < 3.1.0

Weakness: CWE-79 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

References

https://github.com/gofiber/fiber/security/advisories/GHSA-qjv7-627w-8qjv x_refsource_CONFIRM