CVE-2026-25899 Fiber is Vulnerable to Denial of Service via Flash Cookie Unbounded Allocation
An attacker can cause a denial of service by sending a crafted cookie that triggers unbounded memory allocation in the Fiber web framework.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-25899?
CVE-2026-25899 is a high-severity denial of service vulnerability in gofiber fiber, published on 24 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Fiber is an Express inspired web framework written in Go. In versions on the v3 branch prior to 3.1.0, the use of the `fiber_flash` cookie can force an unbounded allocation on any server. A crafted 10-character cookie value triggers an attempt to allocate up to 85GB of memory via unvalidated msgpack deserialization. No authentication is required. Every GoFiber v3 endpoint is affected regardless of whether the application uses flash messages. Version 3.1.0 fixes the issue.
Which versions are affected by CVE-2026-25899?
3 open source packages ship an affected version, including github.com/gofiber/fiber/v3. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/gofiber/fiber/v3 Go | All versions | 3.1.0 |
github.com/gofiber/fiber/v3 Go | All versions | 3.1.0 |
github.com/gofiber/fiber/v3 Go | All versions | 3.1.0 |
Products include Gofiber Fiber.
How do I fix CVE-2026-25899?
Upgrade github.com/gofiber/fiber/v3 to 3.1.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-25899 being exploited?
There is no known exploitation of CVE-2026-25899 in the wild and no public exploit code.
Other vulnerabilities in gofiber fiber
- CVE-2024-38513 Fiber Session Middleware Token Injection Vulnerability
- CVE-2023-45128 CSRF Token Reuse Vulnerability in fiber
- CVE-2024-25124 Fiber has Insecure CORS Configuration, Allowing Wildcard Origin with Credentials
- CVE-2025-66630 Fiber insecurely fallsback in utils.UUIDv4() / utils.UUID() — predictable / zero‑UUID on crypto/rand failure
- CVE-2025-54801 Fiber Susceptible to Crash via `BodyParser` Due to Unvalidated Large Slice Index in Decoder
Sources
Also known as GHSA-2mr3-m5q5-wgp6, GO-2026-4534.