High severity · published Feb 24, 2026
CVE-2026-25899
Fiber is Vulnerable to Denial of Service via Flash Cookie Unbounded Allocation
7.5
CVSS
0.4%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 39% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FI
fiber · gofiber
>= 3.0.0, < 3.1.0 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-25899
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-25899
Release Notes
https://github.com/gofiber/fiber/releases/tag/v3.1.0
Exploit
https://github.com/gofiber/fiber/security/advisories/GHSA-2mr3-m5q5-wgp6
More from fiber
9.8
CVE-2024-38513
Fiber is an Express-inspired web framework written in Go A vulnerability present in versions prior to 2.52.5 is a session middleware issue in GoFiber versions 2 and above
9.8
CVE-2024-25124
Fiber is a web framework written in go
9.4
CVE-2025-66630
Fiber insecurely fallsback in utils.UUIDv4() / utils.UUID() — predictable / zero‑UUID on crypto/rand failure
8.8
CVE-2023-45141
Fiber is an express inspired web framework written in Go
8.8
CVE-2023-45128
Fiber is an express inspired web framework written in Go