# 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.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Feb 2026
- **Updated:** 24 Feb 2026
- **Also known as:** GHSA-2mr3-m5q5-wgp6, GO-2026-4534

## 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.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-789 (Memory Allocation with Excessive Size Value)

## 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 | Ecosystem | 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: Gofiber Fiber.

## How do I fix CVE-2026-25899?

Upgrade github.com/gofiber/fiber/v3 to 3.1.0 or later.

## 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](https://insights.sbomify.com/CVE-2024-38513/): Fiber Session Middleware Token Injection Vulnerability (critical 10.0)
- [CVE-2023-45128](https://insights.sbomify.com/CVE-2023-45128/): CSRF Token Reuse Vulnerability in fiber (critical 10.0)
- [CVE-2024-25124](https://insights.sbomify.com/CVE-2024-25124/): Fiber has Insecure CORS Configuration, Allowing Wildcard Origin with Credentials (critical 9.4)
- [CVE-2025-66630](https://insights.sbomify.com/CVE-2025-66630/): Fiber insecurely fallsback in utils.UUIDv4() / utils.UUID() — predictable / zero‑UUID on crypto/rand failure (critical 9.2)
- [CVE-2025-54801](https://insights.sbomify.com/CVE-2025-54801/): Fiber Susceptible to Crash via `BodyParser` Due to Unvalidated Large Slice Index in Decoder (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-25899 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-25899 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/gofiber/fiber/v3 (Go): affected all versions; fixed in 3.1.0
- github.com/gofiber/fiber/v3 (Go): affected all versions; fixed in 3.1.0
- github.com/gofiber/fiber/v3 (Go): affected all versions; fixed in 3.1.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-25899/ (Markdown: https://insights.sbomify.com/CVE-2026-25899/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-25899
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-25899
- OSV: https://osv.dev/vulnerability/CVE-2026-25899

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-25899/
Summaries are generated and may contain mistakes; the official description above is the record.