CVE-2026-45045

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

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

• 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

CVE-2026-45045 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.3.0); upgrading removes the vulnerable code path.

Kodem intelligence

Replace Header.Add() with Header.Set() at line 282:

c.Request().Header.Set("X-Real-IP", c.IP())

Header.Set() replaces any existing header value, ensuring only the real client IP is forwarded.

1. What is CVE-2026-45045? CVE-2026-45045 is a medium-severity security vulnerability in github.com/gofiber/fiber/v3 (go), affecting versions <= 3.2.0. It is fixed in 3.3.0.
2. How severe is CVE-2026-45045? CVE-2026-45045 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-45045?
   • github.com/gofiber/fiber/v3 (go) (versions <= 3.2.0)
   • github.com/gofiber/fiber/v2 (go) (versions <= 2.52.13)
4. Is there a fix for CVE-2026-45045? Yes. CVE-2026-45045 is fixed in 3.3.0. Upgrade to this version or later.
5. Is CVE-2026-45045 exploitable, and should I be worried? Whether CVE-2026-45045 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-45045 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-45045? Upgrade github.com/gofiber/fiber/v3 to 3.3.0 or later.