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

> Attackers can bypass OAuth redirect validation to steal authorization codes, leading to account takeover and token theft.

- **Severity:** High 8.8 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 25 Aug 2026
- **Updated:** 25 Aug 2026
- **Also known as:** GHSA-m5w8-4879-f4pc, GHSA-p64j-f4x9-wq66, GO-2026-5531

## What is CVE-2026-79662?

CVE-2026-79662 is a high-severity vulnerability in lin-snow Ech0, published on 25 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-601 (URL Redirection to Untrusted Site)

## Which versions are affected by CVE-2026-79662?

3 open source packages ship an affected version, including github.com/lin-snow/Ech0 and github.com/lin-snow/ech0.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/lin-snow/Ech0` | Go | All versions | 1.4.8-0.20260503040728-a7e8b8e84bd1 |
| `github.com/lin-snow/Ech0` | Go | All versions | 1.4.8-0.20260503040728-a7e8b8e84bd1 |
| `github.com/lin-snow/ech0` | Go | All versions | 1.4.8-0.20260503040728-a7e8b8e84bd1 |

## How do I fix CVE-2026-79662?

Upgrade github.com/lin-snow/Ech0 to 1.4.8-0.20260503040728-a7e8b8e84bd1 or later.

## Is CVE-2026-79662 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-79662 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-79662 and fix it if it is affected.

What it is: CVE-2026-79662 is a high-severity vulnerability in lin-snow Ech0, published on 25 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-79662 exists.

Affected packages and fixed versions:
- github.com/lin-snow/Ech0 (Go): affected all versions; fixed in 1.4.8-0.20260503040728-a7e8b8e84bd1
- github.com/lin-snow/Ech0 (Go): affected all versions; fixed in 1.4.8-0.20260503040728-a7e8b8e84bd1
- github.com/lin-snow/ech0 (Go): affected all versions; fixed in 1.4.8-0.20260503040728-a7e8b8e84bd1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-79662/ (Markdown: https://insights.sbomify.com/CVE-2026-79662/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-79662
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-79662
- OSV: https://osv.dev/vulnerability/CVE-2026-79662

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-79662/
Summaries are generated and may contain mistakes; the official description above is the record.