CVE-2026-42554

Fiber is an Express-inspired web framework written in Go. From 2.52.1 until 2.52.3, the CORS middleware's validateDomain wildcard matcher in middleware/cors/utils.go strips the scheme and checks only a host suffix without requiring a dot boundary. An application configured with a wildcard-subdomain AllowOrigins value and AllowCredentials enabled can reflect an unrelated attacker-controlled origin whose host merely ends with the configured base domain.

In the Fiber web framework for Go prior to version 3.4.0, the helmet middleware incorrectly checks the protocol using c.Protocol() instead of c.Scheme(), causing the Strict-Transport-Security header to never be set even when HSTSMaxAge is configured. This issue is fixed in version 3.4.0.

In the Fiber web framework for Go, prior to versions 3.3.0 and 2.52.14, the BalancerForward proxy helper in middleware/proxy/proxy.go uses Header.Add() instead of Header.Set() when injecting the X-Real-IP header. This allows an attacker to supply a first X-Real-IP value that gets forwarded to upstream servers for logging, rate limiting, and access control.

In the Fiber web framework for Go prior to version 3.3.0, the default Authorizer function in the BasicAuth middleware uses short-circuit evaluation that skips password hash comparison for non-existent usernames. This allows reliable remote username enumeration through response timing differences.

In the Fiber web framework for Go through version 3.1.0, the default key generator in the cache middleware uses only the request path and omits the query string. As a result, requests to the same path with different query parameters can share a cache key and receive the wrong cached response. The issue is fixed after version 3.1.0.