# CVE-2026-4438: gethostbyaddr and gethostbyaddr_r return invalid DNS hostnames

> Attackers can trigger invalid DNS hostname returns in glibc when specific nsswitch.conf configurations are used, potentially causing application errors.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Mar 2026
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-80282, BELL-CVE-2026-4438, DEBIAN-CVE-2026-4438, ECHO-49d5-1f6e-5068, GHSA-935r-rfch-9mr7, MINI-23p3-qw4q-3336, MINI-jxmh-jx7m-2j7f, MINI-w92c-xjcr-rg4g, ROOT-OS-UBUNTU-2204-CVE-2026-4438, UBUNTU-CVE-2026-4438

## What is CVE-2026-4438?

CVE-2026-4438 is a medium-severity vulnerability in Gnu Glibc, published on 20 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Calling gethostbyaddr or gethostbyaddr_r with a configured nsswitch.conf that specifies the library's DNS backend in the GNU C library version 2.34 to version 2.43 could result in an invalid DNS hostname being returned to the caller in violation of the DNS specification.

Weakness: CWE-88 (Improper Neutralization of Argument Delimiters in a Command), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-4438?

It affects 1 product.


Products: Gnu Glibc.

## How do I fix CVE-2026-4438?

Upgrade to a fixed version.

## Is CVE-2026-4438 being exploited?

There is no known exploitation of CVE-2026-4438 in the wild and no public exploit code.

## Other vulnerabilities in Gnu Glibc

- [CVE-2026-5450](https://insights.sbomify.com/CVE-2026-5450/): scanf %mc off-by-one heap buffer overflow (critical 9.8)
- [CVE-2023-25139](https://insights.sbomify.com/CVE-2023-25139/): Memory corruption in n/a (critical 9.8)
- [CVE-1999-0199](https://insights.sbomify.com/CVE-1999-0199/): Other in n/a (critical 9.8)
- [CVE-2019-1010022](https://insights.sbomify.com/CVE-2019-1010022/): Security feature bypass in glibc (critical 9.8)
- [CVE-2005-3590](https://insights.sbomify.com/CVE-2005-3590/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-4438 and fix it if it is affected.

What it is: CVE-2026-4438 is a medium-severity vulnerability in Gnu Glibc, published on 20 Mar 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-2026-4438 in the wild and no public exploit code.

Affected product: Gnu Glibc. 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-2026-4438/ (Markdown: https://insights.sbomify.com/CVE-2026-4438/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-4438
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-4438
- OSV: https://osv.dev/vulnerability/CVE-2026-4438

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-4438/
Summaries are generated and may contain mistakes; the official description above is the record.