XSS in Gofiber Fiber
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.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (21.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 21st percentile — 21.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001
Affected products
- Gofiber Fiber — versions < 2.52.13, >= 3.0.0-beta.2, < 3.1.0
Weakness classification (CWE)
References
- github.com/gofiber/fiber/security/advisories/GHSA-qjv7-627w-8qjv (Exploit, Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-42554?
- CVE-2026-42554 is a medium-severity vulnerability in Gofiber Fiber, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-05-11.
- How severe is CVE-2026-42554?
- Medium severity. CVSS v3 base score is 6.1 out of 10.