PT-2026-55275 · Go · Github.Com/Gofiber/Fiber/V2+1

Publicado

2026-07-02

·

Atualizado

2026-07-02

·

CVE-2026-45045

CVSS v3.1

5.3

Média

VetorAV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Summary

The BalancerForward proxy helper in GoFiber uses Header.Add() instead of Header.Set() when injecting the X-Real-IP header. This appends the real client IP as a second header value rather than replacing any attacker-supplied value. Upstream servers that read the first X-Real-IP header (nginx, Express, most HTTP servers) use the attacker's spoofed IP for logging, rate limiting, and access control.

Vulnerable Code

File: middleware/proxy/proxy.go, lines 270-285
go
func BalancerForward(servers []string, clients ...*fasthttp.Client) fiber.Handler {
  r := &roundrobin{
    current: 0,
    pool:  servers,
  }
  return func(c fiber.Ctx) error {
    server := r.get()
    if !strings.HasPrefix(server, "http") {
      server = "http://" + server
    }
    c.Request().Header.Add("X-Real-IP", c.IP())  // line 282: Add, not Set
    return Do(c, server+c.OriginalURL(), clients...)
  }
}

Data Flow

  1. Attacker sends request with X-Real-IP: 10.0.0.1 (spoofed internal IP)
  2. BalancerForward handler executes at line 282
  3. c.Request().Header.Add("X-Real-IP", c.IP()) APPENDS the real IP as a second header
  4. Upstream server receives: X-Real-IP: 10.0.0.1 AND X-Real-IP: <real-attacker-ip>
  5. Most HTTP servers (nginx, Node.js, Apache) read the FIRST value
  6. Upstream uses 10.0.0.1 for all IP-dependent logic

Impact

  • Rate limit bypass: IP-based rate limiting at the upstream uses the spoofed IP, allowing unlimited requests
  • IP ACL bypass: Internal IP allowlists (e.g., admin panels restricted to 10.0.0.0/8) can be bypassed
  • Audit log poisoning: Security logs record the spoofed IP, making incident investigation unreliable
  • Geolocation bypass: IP-based geofencing or region restrictions are circumvented

Fix

Replace Header.Add() with Header.Set() at line 282:
go
c.Request().Header.Set("X-Real-IP", c.IP())
Header.Set() replaces any existing header value, ensuring only the real client IP is forwarded.

Correção

Authentication Bypass by Spoofing

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Enumeração de Fraquezas

CWE-290

Identificadores relacionados

CVE-2026-45045
GHSA-GCFQ-8GQF-4876

Produtos afetados

Github.Com/Gofiber/Fiber/V2
Github.Com/Gofiber/Fiber/V3