Fiber has an Arbitrary File Read in Static Middleware on Windows

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:H/VI:N/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-25891: 0.70% estimated exploitation activity in the next 30 days; percentile 53.33 (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.

Summary Description A Path Traversal (CWE-22) vulnerability in Fiber allows a remote attacker to bypass the static middleware sanitizer and read arbitrary files on the server file system on Windows. This affects Fiber v3 through version 3.0.0. This has been patched in Fiber v3 version 3.1.0. Details The vulnerability resides in middleware/static/static.go within the sanitizePath function. This function attempts to sanitize the requested path by checking for backslashes, decoding the URL, and then cleaning the path. The vulnerability stems from two combined issues: - The check for backslash characters happens before the URL decoding loop. If an attacker sends a double-encoded backslash, the initial check sees %255C and passes. The loop then decodes this into a single backslash. - The function uses path.Clean to clean the resulting string. path.Clean is designed for slash-separated paths and does not recognize backslashes as directory separators. Consequently, sequences like ..\..\ are…

Published by the source

24 Feb 2026, 20:51 UTC

Last modified by the source

27 Feb 2026, 20:04 UTC

Source last checked

26 Oct 2026, 15:14 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-m3c2-496v-cw3v

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# Patch Next advisory brief: CVE-2026-25891

Advisory: Fiber has an Arbitrary File Read in Static Middleware on Windows
IDs: CVE-2026-25891, GHSA-m3c2-496v-cw3v
Record: https://patchnext.com/advisories/cve-2026-25891 (revision 1, source checked 26 Oct 2026, 15:14 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/v3 3.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/gofiber/fiber/v3: affected <= 3.0.0; fixed in 3.1.0

## Suggested inspection (read-only)
- Go github.com/gofiber/fiber/v3: 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/v3.
- 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-m3c2-496v-cw3v (GitHub-reviewed advisory GHSA-m3c2-496v-cw3v lists affected ranges: Go github.com/gofiber/fiber/v3 >=0 <=3.0.0)

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