# CVE-2026-6042: musl libc GB18030 4-byte Decoder iconv.c iconv algorithmic complexity

> A local attacker can cause denial of service in musl libc via inefficient algorithmic complexity in the GB18030 iconv decoder.

- **Severity:** Medium 4.8 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Apr 2026
- **Updated:** 10 Apr 2026
- **Also known as:** ALPINE-CVE-2026-6042, BELL-CVE-2026-6042, DEBIAN-CVE-2026-6042, ECHO-7274-4b19-c757, GHSA-2qh3-3rmv-x43w, ROOT-OS-ALPINE-317-CVE-2026-6042, UBUNTU-CVE-2026-6042

## What is CVE-2026-6042?

CVE-2026-6042 is a medium-severity denial of service vulnerability in musl libc, published on 10 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A security flaw has been discovered in musl libc up to 1.2.6. Affected is the function iconv of the file src/locale/iconv.c of the component GB18030 4-byte Decoder. Performing a manipulation results in inefficient algorithmic complexity. The attack must be initiated from a local position. To fix this issue, it is recommended to deploy a patch.

Weakness: CWE-407 (Inefficient Algorithmic Complexity), CWE-404 (Improper Resource Shutdown or Release)

## Which versions are affected by CVE-2026-6042?


## How do I fix CVE-2026-6042?

Apply the vendor's patch.

## Is CVE-2026-6042 being exploited?

There is no known exploitation of CVE-2026-6042 in the wild and no public exploit code.

Public exploit code:

- Proof of concept and end-to-end test of Algorithmic Complexity DoS in musl libc 0.8.0-1.2.6 assigned CVE-2026-6042 (github_poc): https://github.com/jensnesten/CVE-2026-6042-PoC

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6042 and fix it if it is affected.

What it is: CVE-2026-6042 is a medium-severity denial of service vulnerability in musl libc, published on 10 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-6042 in the wild and no public exploit code.

Affected product: musl libc. 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-2026-6042/ (Markdown: https://insights.sbomify.com/CVE-2026-6042/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6042
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6042
- OSV: https://osv.dev/vulnerability/CVE-2026-6042

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-6042/
Summaries are generated and may contain mistakes; the official description above is the record.