# CVE-2016-6263: The stringprep_utf8_nfkc_normalize function in lib/nfkc.c in libidn before 1.33 allows context-dependent attackers to cause a denial of serv


- **Severity:** High 7.5 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 7 Sep 2016
- **Updated:** 6 Aug 2024
- **Also known as:** ALPINE-CVE-2016-6263, DEBIAN-CVE-2016-6263, GHSA-4q6w-2734-9q8x, UBUNTU-CVE-2016-6263

## What is CVE-2016-6263?

CVE-2016-6263 is a high-severity vulnerability in n/a, published on 7 Sep 2016. 

### Official description

The stringprep_utf8_nfkc_normalize function in lib/nfkc.c in libidn before 1.33 allows context-dependent attackers to cause a denial of service (out-of-bounds read and crash) via crafted UTF-8 data.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2016-6263?

It affects 1 product.


Products: Gnu Libidn.

## How do I fix CVE-2016-6263?

Upgrade to a fixed version.

## Is CVE-2016-6263 being exploited?

There is no known exploitation of CVE-2016-6263 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2026-57053](https://insights.sbomify.com/CVE-2026-57053/): Information disclosure in libidn (medium 4.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2016-6263 and fix it if it is affected.

What it is: CVE-2016-6263 is a high-severity vulnerability in n/a, published on 7 Sep 2016. 
Exploitation: There is no known exploitation of CVE-2016-6263 in the wild and no public exploit code.

Affected product: n/a. 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-2016-6263/ (Markdown: https://insights.sbomify.com/CVE-2016-6263/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2016-6263
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2016-6263
- OSV: https://osv.dev/vulnerability/CVE-2016-6263

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From sbomify Insights: https://insights.sbomify.com/CVE-2016-6263/
Summaries are generated and may contain mistakes; the official description above is the record.