Vulnerability · Published Feb 24, 2026 · Assigned by GitHub_M

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

High 7.5

In plain English

A high-severity security flaw in fiber from gofiber. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 39% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.4%top 60.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/gofiber/fiber/v3	3.1.0	GHSA-2mr3-m5q5-wgp6
Go	github.com/gofiber/fiber/v3	3.1.0	GO-2026-4534

Affected products (as reported)

Vendor	Product	Versions
gofiber	fiber	>= 3.0.0, < 3.1.0

Weakness: CWE-789 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

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