CVE-2025-54801: Fiber Susceptible to Crash via `BodyParser` Due to Unvalidated Large Slice Index in Decoder

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-08-06 · updated 2026-06-17
Weakness: CWE-789

Description

Fiber is an Express inspired web framework written in Go. 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. The root cause is that the decoder attempts to allocate a slice of length idx + 1 without validating whether the index is within a safe or reasonable range. If the idx is excessively large, this leads to an integer overflow or memory exhaustion, causing a panic or crash. This is fixed in version 2.52.9.

Affected products

gofiber fiber: before 2.52.9 — fixed in 2.52.9

How to fix

Upgrade to a fixed version: gofiber fiber 2.52.9. Check the vendor advisory for mitigations.

References

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