Echo has Open Redirect via Control-Character Prefix Defeating sanitizeURI

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-2026-118656: 0.20% estimated exploitation activity in the next 30 days; percentile 9.48 (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 Echo's dedicated open-redirect guard, `sanitizeURI`, decides whether a redirect target is a local path by inspecting exactly two byte positions: `uri[0]` and `uri[1]`. If the value begins with a control character such as a tab or a newline, followed by a separator pair, the guard does not fire and the value is written to the `Location` header unchanged. Browsers remove tab and newline characters from URLs before parsing them, and treat a backslash as a forward slash for HTTP and HTTPS URLs. A `Location` value of ``/\t/attacker.example`` is therefore resolved by the browser as an absolute URL on `attacker.example`. Confirmed end to end in a headless browser.

Technical background

The guard `middleware/slash.go:144` (duplicated verbatim at `echo.go:958`): ```go func sanitizeURI(uri string) string { // double slash `\\`, `//` or even `\/` is absolute uri for browsers and by redirecting request to that uri // we are vulnerable to open redirect attack. so replace all…

Published by the source

28 Oct 2026, 21:04 UTC

Last modified by the source

28 Oct 2026, 21:15 UTC

Source last checked

29 Oct 2026, 06:45 UTC

1. Revision 2 · amended · 29 Oct 2026

   Amended from osv record GHSA-v753-g4cw-jm48

2. Revision 1 · created · 28 Oct 2026

   Published from ghsa record GHSA-v753-g4cw-jm48

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# Patch Next advisory brief: CVE-2026-118656

Advisory: Echo has Open Redirect via Control-Character Prefix Defeating sanitizeURI
IDs: CVE-2026-118656, GHSA-v753-g4cw-jm48
Record: https://patchnext.com/advisories/cve-2026-118656 (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-v753-g4cw-jm48 (GitHub-reviewed advisory GHSA-v753-g4cw-jm48 lists affected ranges: Go github.com/labstack/echo/v5 >=0 =0 <4.16.0)
- Verified: https://osv.dev/vulnerability/GHSA-v753-g4cw-jm48 (OSV record GHSA-v753-g4cw-jm48 lists affected ranges: Go github.com/labstack/echo/v5 >=0 =0 <4.16.0 (fixed))

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