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

Vulnerability summary

CVE-2026-25899 is a high (CVSS 7.5) vulnerability in gofiber fiber. EPSS estimates a 0.70% chance of exploitation in the next 30 days, higher than 52.7% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 24-02-2026
   PublishedVulnerability first disclosed.
2. 24-02-2026
   Last modifiedVulnerability information updated.

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.

• CWE-789Memory Allocation with Excessive Size ValueThe product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated.
• CWE-770Allocation of Resources Without Limits or ThrottlingThe product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.