# CVE-2026-79658: Ech0 before 5.0.1 Denial of Service via Accept-Language

> An unauthenticated attacker can cause denial of service by sending large Accept-Language headers with underscores, triggering quadratic-time parsing in the Ech0 library.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 25 Aug 2026
- **Updated:** 8 Oct 2026
- **Also known as:** GHSA-j8jc-x8v7-x64g

## What is CVE-2026-79658?

CVE-2026-79658 is a high-severity denial of service vulnerability in lin-snow Ech0, published on 25 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Ech0 before 5.0.1 does not impose any size or shape limit on the Accept-Language header processed by its i18n middleware, which runs on every HTTP request. The header is passed unfiltered to go-i18n's NewLocalizer, which internally calls golang.org/x/text/language.ParseAcceptLanguage. The CVE-2022-32149 mitigation in x/text caps '-' characters but not '_' characters, which the parser aliases to '-', allowing quadratic-time parsing to be triggered with a large header (up to Go's default 1 MiB) built from underscore separators. An unauthenticated attacker can send such requests to consume roughly 1.5 seconds of CPU each, and concurrent requests can saturate a multi-core server (denial of service).

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-79658?


## How do I fix CVE-2026-79658?

No fix has been published for CVE-2026-79658 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-79658 being exploited?

There is no known exploitation of CVE-2026-79658 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-79658 and fix it if it is affected.

What it is: CVE-2026-79658 is a high-severity denial of service vulnerability in lin-snow Ech0, published on 25 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-79658 in the wild and no public exploit code.

Affected product: lin-snow Ech0. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-79658/ (Markdown: https://insights.sbomify.com/CVE-2026-79658/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-79658
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-79658
- OSV: https://osv.dev/vulnerability/CVE-2026-79658

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-79658/
Summaries are generated and may contain mistakes; the official description above is the record.