What’s Vulnerable › Vulnerabilities

CVE-2026-25899: Fiber is Vulnerable to Denial of Service via Flash Cookie Unbounded Allocation

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-02-24 · updated 2026-06-17
• Weakness: CWE-789

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.

Affected products

• gofiber fiber: from 3.0.0 before 3.1.0 — fixed in 3.1.0

How to fix

Upgrade to a fixed version: gofiber fiber 3.1.0. Check the vendor advisory for mitigations.

References

• https://github.com/gofiber/fiber/releases/tag/v3.1.0
• https://github.com/gofiber/fiber/security/advisories/GHSA-2mr3-m5q5-wgp6

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