Fiber Crashes in BodyParser Due to Unvalidated Large Slice Index in Decoder

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2025-54801: 0.40% estimated exploitation activity in the next 30 days; percentile 33.76 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Description 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 idx is excessively large, this leads to an integer overflow or memory exhaustion, causing a panic or crash. Steps to Reproduce Create a POST request handler that accepts x-www-form-urlencoded data Run the server and send a POST request with a large numeric key in form data, such as: Relevant Code Snippet Within the decoder's decode method: The idx is not validated before use, leading to unsafe slice allocation for extremely large values. --- Impact - Application panic or crash on malicious or malformed input. - Potential denial of service (DoS) via memory exhaustion or server…

Published by the source

5 Aug 2025, 15:22 UTC

Last modified by the source

6 Aug 2025, 14:31 UTC

Source last checked

26 Oct 2026, 15:10 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-qx2q-88mx-vhg7

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# Patch Next advisory brief: CVE-2025-54801

Advisory: Fiber Crashes in BodyParser Due to Unvalidated Large Slice Index in Decoder
IDs: CVE-2025-54801, GHSA-qx2q-88mx-vhg7
Record: https://patchnext.com/advisories/cve-2025-54801 (revision 1, source checked 26 Oct 2026, 15:10 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/gofiber/fiber/v2 2.52.9. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/gofiber/fiber/v2: affected <= 2.52.8; fixed in 2.52.9

## Suggested inspection (read-only)
- Go github.com/gofiber/fiber/v2: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/gofiber/fiber/v2.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-qx2q-88mx-vhg7 (GitHub-reviewed advisory GHSA-qx2q-88mx-vhg7 lists affected ranges: Go github.com/gofiber/fiber/v2 >=0 <=2.52.8)

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