Ech0's RSS feed renders unescaped tag names and raw-HTML markdown, stored XSS against subscribers

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 public RSS/Atom feed at /rss renders two attacker-controlled surfaces without HTML escaping. Tag names flow through fmt.Appendf(renderedContent, "<br /<span class=\"tag\"#%s</span", tag.Name) at internal/service/common/common.go:120, and the Markdown renderer at internal/util/md/md.go does not set the html.SkipHTML flag, so raw HTML blocks in echo content pass through unmodified. The resulting Atom <summary type="html" is valid XML but contains executable <script tags after the RSS reader decodes it. RSS subscribers whose readers render HTML (including many self-hosted and desktop clients) execute attacker JavaScript in the reader's origin. Details Tag sink at internal/service/common/common.go:120: fmt.Appendf with %s does not HTML-escape. Tag names come from user-supplied EchoUpsertDto.Tags and are persisted after strings.TrimSpace(strings.TrimPrefix(tag.Name, "#")) at internal/service/echo/echo.go:326, which strips a leading

and trims whitespace but does nothing about…

Published by the source

7 May 2026, 21:18 UTC

Last modified by the source

7 May 2026, 21:18 UTC

Source last checked

26 Oct 2026, 15:20 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-3v85-fqvh-7rxf

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# Patch Next advisory brief: GHSA-3v85-fqvh-7rxf

Advisory: Ech0's RSS feed renders unescaped tag names and raw-HTML markdown, stored XSS against subscribers
IDs: GHSA-3v85-fqvh-7rxf
Record: https://patchnext.com/advisories/ghsa-3v85-fqvh-7rxf (revision 1, source checked 26 Oct 2026, 15:20 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 1.4.8-0.20260503035519-fd320fe3e902. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/lin-snow/Ech0: affected < 1.4.8-0.20260503035519-fd320fe3e902; fixed in 1.4.8-0.20260503035519-fd320fe3e902

## 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-3v85-fqvh-7rxf (GitHub-reviewed advisory GHSA-3v85-fqvh-7rxf lists affected ranges: Go github.com/lin-snow/Ech0 >=0 <1.4.8-0.20260503035519-fd320fe3e902)

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