GHSA-g5jq-qmqr-qrwf Fiber: CORS wildcard origins matched without a dot boundary, allowing credentialed cross-origin reads

• Go github.com/gofiber/fiber/v2: >= 2.52.1, < 2.52.3 → fixed in 2.52.3

Summary In v2.52.1 and v2.52.2 the CORS middleware matched a wildcard origin such as `https://*.example.com` by suffix only, without a dot boundary and without comparing the scheme. Any origin whose host ends with the base domain, for example `https://evil-example.com` or `http://notexample.com`, was reflected in `Access-Control-Allow-Origin`, together with `Access-Control-Allow-Credentials: true` when `AllowCredentials` is enabled. v2.52.3 replaced the matcher (#2915) and is not affected. The report was filed against v2.52.15, where the dot boundary holds; see "Other versions" below. Details v2.52.1 introduced `validateDomain` in `middleware/cors/utils.go` (f0cd3b44, part of the fix for GHSA-fmg4-x8pw-hjhg). It strips scheme and port from both sides and then checks only the suffix, with `trimmedPattern = "example.com"`, so the character before the suffix is never checked: ```go if strings.HasPrefix(normalizedPattern, "*.") { trimmedPattern := normalizedPattern[2:] if strings.HasSuffix(normalizedDomain, trimmedPattern) { if normalizedDomain != trimmedPattern { if strings.TrimSuffix(normalizedDomain, trimmedPattern) != "" { return true } } } } ``` v2.52.3 (1aac6f61, #2915) replaced it with a scheme-aware prefix/suffix split that keeps the leading dot in the suffix (`.example.com`). Proof of concept ```go app := fiber.New() app.Use(cors.New(cors.Config{ AllowOrigins: "https://*.example.com", AllowCredentials: true, })) app.Get("/", func(c *fiber.Ctx) error { return c.SendString("secret") }) ``` Request with `Origin: https://evil-example.com`, as a GET and as a preflight (`OPTIONS` with `Access-Control-Request-Method: GET`): | Version | `https://evil-example.com` | `http://evil-example.com` | |---|---|---| | v2.52.0 | not allowed | not allowed | | v2.52.1, v2.52.2 | reflected, `Access-Control-Allow-Credentials: true` | reflected, `Access-Control-Allow-Credentials: true` | | v2.52.3 to v2.52.16 | not allowed | not allowed | Impact An app that configures a wildcard-subdomain `AllowOrigins` with `AllowCredentials: true` lets any page on a domain that ends with the base domain (for example `notexample.com` for `*.example.com`) read authenticated responses cross-origin. Fixed in v2.52.3; upgrade to the latest v2 release. Other versions All v2 releases before v2.52.16 also accepted origins with empty labels (`https://.example.com`, `https://a..example.com`), and v2.52.3 to v2.52.15 mis-parsed a wildcard entry after a comma and a space (`"https://a.com, https://*.example.com"`). No registrable domain produces such an origin, so these are hardening rather than part of this advisory. They are fixed in v2.52.16 (#4792).