CVE-2026-25899
📋 TL;DR
CVE-2026-25899 is a memory exhaustion vulnerability in GoFiber v3 web framework where a specially crafted 10-character cookie value triggers unvalidated msgpack deserialization, attempting to allocate up to 85GB of memory. All GoFiber v3 endpoints are vulnerable regardless of whether the application uses flash messages, and no authentication is required. This affects any server running vulnerable GoFiber v3 applications.
💻 Affected Systems
- GoFiber
📦 What is this software?
Fiber by Gofiber
⚠️ Risk & Real-World Impact
Worst Case
Complete denial of service through memory exhaustion causing server crashes, potentially leading to service unavailability and resource exhaustion attacks.
Likely Case
Denial of service attacks causing application instability, increased memory usage, and potential service disruption.
If Mitigated
Minimal impact with proper input validation and memory limits in place, though the core vulnerability remains.
🎯 Exploit Status
Exploitation requires sending a specially crafted 10-character cookie value. No authentication required and exploit is simple to execute.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.1.0
Vendor Advisory: https://github.com/gofiber/fiber/security/advisories/GHSA-2mr3-m5q5-wgp6
Restart Required: Yes
Instructions:
1. Update GoFiber dependency to version 3.1.0 or later. 2. Update go.mod file to require github.com/gofiber/fiber/v3 v3.1.0. 3. Run go mod tidy. 4. Rebuild and redeploy application. 5. Restart the service.
🔧 Temporary Workarounds
Disable flash middleware
allRemove or disable the flash middleware if not required by the application
Remove app.Use(flash.New()) from your GoFiber application code
Implement request filtering
allAdd middleware to filter or reject requests containing fiber_flash cookie
Implement custom middleware to check for and reject requests with fiber_flash cookie
🧯 If You Can't Patch
- Implement WAF rules to block requests containing specially crafted fiber_flash cookies
- Deploy rate limiting and request filtering to mitigate denial of service impact
🔍 How to Verify
Check if Vulnerable:
Check go.mod file for github.com/gofiber/fiber/v3 version. If version is < 3.1.0, the system is vulnerable.Check Version:
grep 'github.com/gofiber/fiber/v3' go.modVerify Fix Applied:
Verify go.mod requires github.com/gofiber/fiber/v3 v3.1.0 or later and run go version -m <binary> to check linked version.📡 Detection & Monitoring
Log Indicators:
- Unusual memory spikes
- Process crashes/OOM kills
- Requests with fiber_flash cookie headers
Network Indicators:
- HTTP requests with specially crafted fiber_flash cookies
- Unusual memory allocation patterns
SIEM Query:
source="web_logs" AND cookie="*fiber_flash*" AND (memory_usage>threshold OR process_status="crashed")