# CVE-2026-71848: Hono: Algorithmic Complexity DoS in Language Middleware

> An attacker can cause excessive CPU consumption and service disruption by sending crafted language tags to applications using the Hono framework's language middleware.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 Aug 2026
- **Updated:** 8 Aug 2026
- **Also known as:** CLEANSTART-2026-KR37060, ECHO-3479-a34e-1fda, GHSA-54fx-42gc-7vw4, MINI-3gvp-78w5-q7cw, MINI-3wwr-w4xh-84pw, MINI-5596-fxvv-prgm, MINI-65xp-h6qh-8c4c, MINI-8vqw-5x2x-hr3j, MINI-m7mg-hj9p-5chw, MINI-m9rv-4xx3-cfpv, MINI-vp35-v2fp-4v7f, MINI-wfxj-57j9-gr9x, MINI-wpf3-8v9r-wh67, MINI-x8q9-vr5w-pp45

## What is CVE-2026-71848?

CVE-2026-71848 is a medium-severity denial of service vulnerability in honojs hono, published on 7 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Hono is a Web application framework that provides support for any JavaScript runtime. From 4.12.0 to 4.12.33, the languageDetector middleware is vulnerable to algorithmic complexity denial of service when processing a crafted language tag containing a large number of hyphen separated subtags. To implement progressive language tag truncation, normalizeLanguage() repeatedly calls parts.slice(0, i).join('-') for every possible prefix, so the total amount of string processing grows quadratically with the number of subtags. Language values may come from a query parameter, cookie, Accept-Language header, or URL path, depending on the detector configuration, and the default detector order enables query string, cookie, and header detection, so applications using languageDetector() may expose this processing to unauthenticated requests. An attacker may repeatedly send requests containing long, hyphen separated language tags, causing excessive CPU consumption and preventing unrelated requests from being processed. This issue is fixed in version 4.12.34.

Weakness: CWE-407 (Inefficient Algorithmic Complexity)

## Which versions are affected by CVE-2026-71848?

2 open source packages ship an affected version, including hono.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hono` | npm | From 4.12.0 | 4.12.34 |
| `hono` | npm | From 4.12.0 | 4.12.34 |

## How do I fix CVE-2026-71848?

Upgrade hono to 4.12.34 or later.

## Is CVE-2026-71848 being exploited?

There is no known exploitation of CVE-2026-71848 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-71848 and fix it if it is affected.

What it is: CVE-2026-71848 is a medium-severity denial of service vulnerability in honojs hono, published on 7 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-2026-71848 in the wild and no public exploit code.

Affected packages and fixed versions:
- hono (npm): affected from 4.12.0; fixed in 4.12.34
- hono (npm): affected from 4.12.0; fixed in 4.12.34

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-2026-71848/ (Markdown: https://insights.sbomify.com/CVE-2026-71848/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-71848
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-71848
- OSV: https://osv.dev/vulnerability/CVE-2026-71848

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-71848/
Summaries are generated and may contain mistakes; the official description above is the record.