Echo vulnerable to Reflected Cross-Site Scripting (XSS) via unsanitized JSONP callback in Context.JSONP / Context.JSONPBlob

Exploitation

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

CVSS

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

EPSS

• CVE-2026-118652: 0.24% estimated exploitation activity in the next 30 days; percentile 15.09 (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 The `Context.JSONP`, `Context.JSONPBlob`, and internal `jsonPBlob` helper in `context.go` directly concatenate the caller-supplied `callback` parameter into a JavaScript response without any validation, escaping, or allow-listing. This creates a high-impact reflected XSS that can be triggered by any route passing attacker-controlled data (query string, form, header, path param, etc.) into the callback. Present in current master and v5.1.0 (latest release).

Vulnerable Code (verbatim) ```go func (c *Context) jsonPBlob(code int, callback string, i any) (err error) { c.writeContentType(MIMEApplicationJavaScriptCharsetUTF8) c.response.WriteHeader(code) if _, err = c.response.Write([]byte(callback + "(")); err != nil { return } if err = c.echo.JSONSerializer.Serialize(c, i, ""); err != nil { return } if _, err = c.response.Write([]byte(");")); err != nil { return } return } func (c *Context) JSONP(code int, callback string, i any) (err error) { return…

Published by the source

28 Oct 2026, 19:54 UTC

Last modified by the source

28 Oct 2026, 20:15 UTC

Source last checked

29 Oct 2026, 06:45 UTC

1. Revision 2 · amended · 29 Oct 2026

   Amended from osv record GHSA-h9g5-28mm-hx3g

2. Revision 1 · created · 28 Oct 2026

   Published from ghsa record GHSA-h9g5-28mm-hx3g

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-118652

Advisory: Echo vulnerable to Reflected Cross-Site Scripting (XSS) via unsanitized JSONP callback in Context.JSONP / Context.JSONPBlob
IDs: CVE-2026-118652, GHSA-h9g5-28mm-hx3g
Record: https://patchnext.com/advisories/cve-2026-118652 (revision 2, source checked 29 Oct 2026, 06:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/labstack/echo/v4 4.16.0; github.com/labstack/echo/v5 5.4.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/labstack/echo/v4: affected < 4.16.0; fixed in 4.16.0
- Go github.com/labstack/echo/v5: affected < 5.4.0; fixed in 5.4.0

## Suggested inspection (read-only)
- Go github.com/labstack/echo/v4: check the installed version with your package manager.
- Go github.com/labstack/echo/v5: 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/labstack/echo/v4, github.com/labstack/echo/v5.
- 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-h9g5-28mm-hx3g (GitHub-reviewed advisory GHSA-h9g5-28mm-hx3g lists affected ranges: Go github.com/labstack/echo/v5 >=0 =0 <4.16.0)
- Verified: https://osv.dev/vulnerability/GHSA-h9g5-28mm-hx3g (OSV record GHSA-h9g5-28mm-hx3g lists affected ranges: Go github.com/labstack/echo/v5 >=0 =0 <4.16.0 (fixed))

Commands are suggestions: review each one before running it.