CVE-2025-48075 in fiber
Summary
by MITRE • 05/22/2025
Fiber is an Express-inspired web framework written in Go. Starting in version 2.52.6 and prior to version 2.52.7, `fiber.Ctx.BodyParser` can map flat data to nested slices using `key[idx]value` syntax, but when idx is negative, it causes a panic instead of returning an error stating it cannot process the data. Since this data is user-provided, this could lead to denial of service for anyone relying on this `fiber.Ctx.BodyParser` functionality. Version 2.52.7 fixes the issue.
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Analysis
by VulDB Data Team • 08/06/2025
The vulnerability identified as CVE-2025-48075 affects the Fiber web framework for Go, specifically within the `fiber.Ctx.BodyParser` functionality. This issue emerged in version 2.52.6 and remained unresolved until the release of version 2.52.7. The core problem lies in how the framework handles data parsing when processing form data with nested slice structures using the `key[idx]value` syntax. The framework correctly processes positive indices but fails to handle negative indices appropriately, leading to a critical runtime panic instead of gracefully handling the malformed input.
The technical flaw represents a classic denial of service vulnerability that exploits improper input validation within the request parsing layer. When a user submits form data containing negative indices in the slice mapping syntax, the BodyParser function attempts to process these values and encounters an out-of-bounds condition that triggers a panic. This panic occurs because the framework does not validate that array indices are non-negative before attempting to access array elements. The issue stems from a lack of proper bounds checking and input sanitization in the parsing logic, which directly violates security best practices for robust input handling.
The operational impact of this vulnerability is significant for applications relying on Fiber's BodyParser functionality, particularly those accepting user-submitted form data. An attacker could craft malicious requests containing negative indices in form field names, causing the application to crash and become unavailable to legitimate users. This creates a straightforward denial of service scenario where a single malformed request can bring down the entire service. The vulnerability affects any application using Fiber versions between 2.52.6 and 2.52.7 that process user-provided form data through the BodyParser function, making it a widespread concern across affected deployments.
This vulnerability maps to CWE-129: Improper Validation of Array Index and CWE-472: External Control of System or Configuration Setting, as it involves improper validation of user-provided indices and represents an external input that controls parsing behavior. From an ATT&CK perspective, this issue falls under T1499.004: Endpoint Denial of Service, specifically targeting application availability through malformed input processing. The fix implemented in version 2.52.7 addresses the core issue by adding proper validation for array indices, ensuring that negative values are rejected with appropriate error messages rather than causing system panics. Organizations should immediately upgrade to version 2.52.7 or later to mitigate this vulnerability and implement additional input validation measures to protect against similar issues in other components of their applications.