Ech0 has Stored XSS via SVG Upload and Content-Type Validation Bypass in File Upload

Exploitation

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

CVSS

4.8 · CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Summary The file upload endpoint validates Content-Type using only the client-supplied multipart header, with no server-side content inspection or file extension validation. Combined with an unauthenticated static file server that determines Content-Type from file extension, this allows an admin to upload HTML/SVG files containing JavaScript that execute in the application's origin when visited by any user. Additionally, image/svg+xml is in the default allowed types, enabling stored XSS via SVG without any Content-Type spoofing. Details The upload handler at internal/service/file/file.go:85-87 validates file type using only the multipart Content-Type header: isAllowedType at file.go:836-843 performs exact string matching — no magic byte detection, no extension validation: The original file extension is preserved in the storage key by RandomKeyGenerator at internal/storage/keygen.go:41: All locally stored files are served publicly without authentication at…

Published by the source

10 Apr 2026, 19:50 UTC

Last modified by the source

10 Apr 2026, 19:50 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-69hx-63pv-f8f4

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# Patch Next advisory brief: GHSA-69hx-63pv-f8f4

Advisory: Ech0 has Stored XSS via SVG Upload and Content-Type Validation Bypass in File Upload
IDs: GHSA-69hx-63pv-f8f4
Record: https://patchnext.com/advisories/ghsa-69hx-63pv-f8f4 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/lin-snow/ech0 4.4.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/lin-snow/ech0: affected < 4.4.3; fixed in 4.4.3

## Suggested inspection (read-only)
- Go github.com/lin-snow/ech0: 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/lin-snow/ech0.
- 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-69hx-63pv-f8f4 (GitHub-reviewed advisory GHSA-69hx-63pv-f8f4 lists affected ranges: Go github.com/lin-snow/ech0 >=0 <4.4.3)

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