CVE-2026-53624: Fiber Framework HSTS Header Not Set

Technical summary

The helmet middleware in Fiber versions prior to 3.4.0 contains a logic error in middleware/helmet/helmet.go where HSTS header configuration is determined by checking c.Protocol() instead of c.Scheme(). The Protocol() method does not reliably indicate HTTPS connections in all request contexts, whereas Scheme() correctly reports the actual protocol used. As a result, when HSTSMaxAge is configured (indicating the developer's intent to enforce HSTS), the Strict-Transport-Security response header is never set. This allows potential attackers to intercept traffic or facilitate downgrade attacks, bypassing the intended HTTPS-only policy. The fix, available in version 3.4.0, corrects the conditional check to use c.Scheme() and ensures HSTS headers are properly emitted when configured.

Business impact

Applications using Fiber versions before 3.4.0 with HSTS configured face reduced security posture without realizing it. Users of affected applications remain exposed to protocol downgrade attacks and man-in-the-middle interception, even though administrators believed they had enabled strict transport security. This creates compliance and liability risks, particularly for organizations handling sensitive data or operating under regulatory requirements like HIPAA, PCI-DSS, or GDPR that mandate encryption controls. The silent failure—where configuration appears correct but doesn't take effect—compounds the risk because the vulnerability is easily missed during security audits.

Affected systems

Gofiber Fiber framework versions prior to 3.4.0 are affected. Any Go application built with Fiber that uses the helmet middleware and has configured HSTSMaxAge is vulnerable, regardless of deployment environment. The vulnerability affects all platforms where Fiber can run (Linux, Windows, macOS, containers). Severity increases for internet-facing applications and those processing authentication tokens or sensitive user data.

Exploitability

Exploitation requires that an attacker be positioned to intercept network traffic between client and server—typically on a shared network, compromised ISP infrastructure, or via DNS hijacking. The attacker would need to downgrade the initial connection attempt from HTTPS to HTTP, which the absence of HSTS headers allows. The CVSS score of 4.8 (Medium) reflects that while the vulnerability itself is real, successful exploitation requires network-adjacent positioning and user-level access (no administrative privilege required). Automated exploitation is unlikely; attacks would be opportunistic against traffic on controlled networks.

Remediation

Upgrade Fiber to version 3.4.0 or later. Verify that your application depends on the patched version in go.mod or go.sum. After upgrading, rebuild and redeploy applications. There is no configuration workaround for earlier versions; code-level fixes are not feasible without updating the framework. For organizations unable to upgrade immediately, consider additional mitigations such as implementing HSTS headers at the reverse proxy or load balancer level (nginx, HAProxy, cloud WAF) to enforce the policy outside the application.

Patch guidance

Update the Fiber dependency in go.mod to version 3.4.0 or later. Run 'go get -u github.com/gofiber/fiber/[email protected]' (verify the exact import path and version against the official Gofiber release notes). Test in a staging environment to ensure compatibility with your application, though this is a low-risk security patch with no breaking changes reported. Update all container images and deployment artifacts after testing. Prioritize patching for internet-exposed services handling authentication or sensitive data.

Detection guidance

Verify the Fiber version in use across your infrastructure by inspecting go.mod files and container image metadata. Review application logs and traffic captures to determine whether Strict-Transport-Security headers are present in HTTPS responses when helmet middleware is active. Use curl or browser developer tools to confirm: 'curl -I https://your-app/' should include 'Strict-Transport-Security: max-age=...' if HSTS is configured. Scan for vulnerable code patterns in configuration files where HSTSMaxAge is set on Fiber instances prior to v3.4.0. Network-based detection is difficult without deep packet inspection; rely on source code and version audits.

Why prioritize this

Although marked Medium severity, prioritize this vulnerability if your application is internet-facing, handles authentication, or processes sensitive data. The silent failure nature—where misconfiguration appears correct—makes it particularly dangerous because it defeats defense-in-depth expectations. Organizations relying on HSTS as a key control for preventing protocol downgrade should patch quickly. If applications are internal-only or already protected by external TLS enforcement (reverse proxy HSTS headers), risk is lower but patching remains prudent.

Risk score, explained

The CVSS 3.1 score of 4.8 reflects: Network-accessible vulnerability (AV:N) with moderately difficult exploitation conditions (AC:H, requiring attacker network positioning), low impact on confidentiality and integrity (C:L, I:L), and no impact on availability (A:N). The score appropriately captures that while the vulnerability is real and exploitable, it requires active network-level attack capability and is not remotely exploitable in a trivial manner. Real-world risk depends heavily on deployment context and whether additional HSTS enforcement exists at the infrastructure layer.

Frequently asked questions