Cross-Site Scripting (XSS) in github.com/gofiber/fiber/v3 (CVE-2026-42554)
Summary
Cross-site scripting in github.com/gofiber/fiber/v3 (CVE-2026-42554). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 3.2.0 or later.
Original description
The description as published by the source.
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.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A weakness called CVE-2026-42554 was discovered in github.com/gofiber/fiber/v3.
In plain terms, it is a flaw that lets attackers sneak nasty scripts into a webpage.
Severity is Medium (CVSS 6.1/10). Exploitation requires specific conditions but can cause real harm if successful.
What you should do: update the affected software to the latest version. If unsure, ask your IT team or search the vendor's site for "github.com/gofiber/fiber/v3 CVE-2026-42554".
CVE-2026-42554 (github.com/gofiber/fiber/v3). Severity: Medium / CVSSv3 6.1. Category: CWE-79.
Response plan:
- Check the vendor advisory for affected versions and the patched release.
- If a vulnerable version is running in production, schedule maintenance (urgency from KEV/CVSS).
- If no patch yet, mitigate via WAF rule, disabling the affected feature, etc.
- Monitor logs / SIEM for known IOC and PoC signatures of this CVE.
PoCs and fix commits: see the 'References' section, MITRE, and NVD.
A weakness (CVE-2026-42554) in github.com/gofiber/fiber/v3. In plain words, it is a flaw that lets attackers sneak nasty scripts into a webpage.
Target versions of github.com/gofiber/fiber/v3 (see vendor advisory). If running in production, identify exposure immediately.
Severity: Medium (CVSS 6.1/10). Exploitation requires specific conditions but can cause real harm if successful.
Update to the patched release as listed in the vendor advisory. (Typical mitigation pattern for CWE-79)
If a patch is not yet available, consider disabling the affected feature, applying WAF rules, blocking via network ACLs, or isolating the vulnerable version.
Check version information, scan dependencies via SBOM, and monitor SIEM for IOC and PoC signatures related to this CVE.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'github.com/gofiber/fiber/v3' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
github.com/gofiber/fiber/v3を grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade github.com/gofiber/fiber/v3 to 3.2.0ステージング環境で 3.2.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- web github.com