Fiber: XSS in AutoFormat Content Negotiation
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.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-42554
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 5 Nov 2026, 01:04 UTC · Revision 1
Source evidence
Fiber: XSS in AutoFormat Content Negotiation
core-osv · Original sourcePublished 11 May 2026, 21:47 UTC
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.
osv:CVE-2026-42554
Complete source record
{
"id": "c9be36543e6009961a4f4ccc51d56222edce1ef42791881907b793f3055287a4",
"url": "https://osv.dev/vulnerability/CVE-2026-42554",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "Fiber: XSS in AutoFormat Content Negotiation",
"summary": "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.",
"evidence": "osv:CVE-2026-42554",
"products": [],
"severity": "medium",
"structured": {
"id": "CVE-2026-42554",
"aliases": [
"CVE-2026-42554",
"GHSA-qjv7-627w-8qjv",
"GO-2026-5585"
],
"metrics": [
{
"type": "CVSS_V4",
"score": "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"
}
],
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"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-42554.json"
}
}
],
"modified": "2026-10-28T02:30:41.527685441Z",
"provider": "osv",
"references": [
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42554.json",
"https://github.com/gofiber/fiber/security/advisories/GHSA-qjv7-627w-8qjv",
"https://nvd.nist.gov/vuln/detail/CVE-2026-42554"
],
"provider_metadata": {
"cwe_ids": [
"CWE-79"
],
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42554.json"
}
},
"related_cves": [
{
"value": "CVE-2026-42554",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 508894,
"published_at": "2026-05-11T21:47:17.133+00:00"
}