CVE-2025-54801: Gofiber Fiber DOS Vulnerability

CVE-2025-54801 Overview

CVE-2025-54801 is a denial of service vulnerability affecting Fiber, an Express-inspired web framework written in Go. The vulnerability exists in versions 2.52.8 and below when using Fiber's Ctx.BodyParser to parse form data containing a large numeric key that represents a slice index (e.g., test.18446744073704). The application crashes due to an out-of-bounds slice allocation in the underlying schema decoder, leading to memory exhaustion or a panic condition.

Critical Impact

Attackers can remotely crash Fiber-based web applications by sending specially crafted form data with excessively large slice index values, causing service disruption without requiring authentication.

Affected Products

• Gofiber Fiber versions 2.52.8 and below
• Applications using Ctx.BodyParser for form data parsing
• Go applications built with the vulnerable Fiber web framework

Discovery Timeline

• 2025-08-06 - CVE-2025-54801 published to NVD
• 2025-09-23 - Last updated in NVD database

Technical Details for CVE-2025-54801

Vulnerability Analysis

This vulnerability is classified under CWE-789 (Memory Allocation with Excessive Size Value), a weakness that occurs when an application allocates memory based on an untrusted size value without proper validation. In Fiber's case, the Ctx.BodyParser function processes form data and relies on a schema decoder to handle structured input. When form field names contain slice indices, the decoder parses the numeric value and attempts to allocate a slice of the corresponding size.

The fundamental issue is the decoder's lack of bounds checking on the slice index value. An attacker can craft a malicious HTTP request with a form field name containing an astronomically large number as a slice index. When the decoder processes this input, it attempts to allocate a slice with idx + 1 elements, where idx is the attacker-controlled value. This leads to either an integer overflow condition or memory exhaustion, ultimately causing the application to panic and crash.

Root Cause

The root cause of CVE-2025-54801 lies in the schema decoder's failure to validate whether a slice index is within a safe or reasonable range before allocation. When parsing form data like test.18446744073704, the decoder extracts the numeric index and directly uses it to allocate a new slice with idx + 1 elements. Since Go's slice allocation requires contiguous memory, requesting an allocation for an excessively large slice either triggers an integer overflow (when idx + 1 wraps around) or exhausts available memory, resulting in a runtime panic that crashes the application.

Attack Vector

The attack vector for this vulnerability is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by sending an HTTP POST request to any endpoint that uses Ctx.BodyParser for form data parsing. The malicious request contains form-encoded data with a field name that includes a large numeric slice index.

The attack is straightforward to execute: the attacker simply needs to craft a form submission where a field name follows the pattern fieldname.LARGE_NUMBER, where LARGE_NUMBER is a value large enough to trigger memory exhaustion. For example, using an index value near the maximum 64-bit integer boundary will cause the application to crash immediately upon parsing.

Since no code examples are available, organizations should consult the GitHub Security Advisory GHSA-qx2q-88mx-vhg7 for detailed technical information about the vulnerability mechanics and the specific fix implemented.

Detection Methods for CVE-2025-54801

Indicators of Compromise

• HTTP POST requests containing form field names with unusually large numeric indices (e.g., fieldname.18446744073709551615)
• Application crashes or panics in Fiber-based services following form data parsing operations
• Memory consumption spikes immediately preceding application termination
• Stack traces indicating slice allocation failures in the schema decoder

Detection Strategies

• Monitor application logs for panic messages related to memory allocation failures or out-of-bounds slice operations
• Implement network-level detection for HTTP requests containing form field names with numeric values exceeding reasonable slice indices (e.g., values greater than 10,000)
• Deploy runtime application self-protection (RASP) solutions to detect abnormal memory allocation patterns
• Use web application firewalls (WAF) to filter requests with suspicious form field naming patterns

Monitoring Recommendations

• Enable detailed logging for Ctx.BodyParser operations in development and staging environments
• Set up alerting for application restarts or crashes that correlate with incoming HTTP requests
• Monitor system memory utilization for sudden allocation spikes on servers running Fiber applications
• Implement distributed tracing to correlate crash events with specific incoming requests

How to Mitigate CVE-2025-54801

Immediate Actions Required

• Upgrade Fiber to version 2.52.9 or later immediately, as this version contains the fix for the vulnerability
• Audit all applications using Fiber to identify endpoints that utilize Ctx.BodyParser for form data handling
• Implement input validation at the application level to reject form field names with excessively large numeric indices
• Consider deploying a WAF rule to block requests with suspicious form field patterns as a temporary measure

Patch Information

The vulnerability is fixed in Fiber version 2.52.9. The fix introduces proper validation of slice indices before allocation, preventing excessively large values from triggering memory exhaustion. Organizations should update their Go module dependencies to pull in the patched version.

The fix is available in commit e115c08b8f059a4a031b492aa9eef0712411853d. For detailed information about the vulnerability and the remediation, refer to the GitHub Security Advisory GHSA-qx2q-88mx-vhg7.

Workarounds

• Implement custom middleware to validate and sanitize form field names before they reach Ctx.BodyParser
• Use input validation to reject any form submissions with field names containing numeric indices above a reasonable threshold
• Consider using alternative parsing methods that do not rely on the vulnerable schema decoder functionality
• Deploy rate limiting on endpoints that accept form data to reduce the impact of potential denial of service attempts

# Update Fiber dependency to patched version
go get github.com/gofiber/fiber/v2@v2.52.9
go mod tidy