# CVE-2026-18839: Popt-devel: popt-static: size_t underflow in singleoptionhelp

> A local attacker can cause a denial of service in applications using the popt library by triggering an integer underflow during help text formatting.

- **Severity:** Low 2.2 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 5 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-94511, AZL-94668, DEBIAN-CVE-2026-18839, ECHO-3ba8-d639-d262, GHSA-8fjx-p4xg-vgp8, OESA-2026-4392, OESA-2026-4393, OESA-2026-4394, OESA-2026-4395, RHSA-2026:77932, UBUNTU-CVE-2026-18839

## What is CVE-2026-18839?

CVE-2026-18839 is a low-severity vulnerability in Red Hat Enterprise Linux 10, published on 5 Aug 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

An integer underflow was found in the popt library when formatting help text for option tables that exceed the terminal width. A local user who can cause an application to print help under those conditions may cause that application to crash or fail to display help, resulting in a denial of service of the affected application.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2026-18839?


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `popt` | Red Hat:hummingbird:1 | All versions | 0:1.19-11.2.hum1 |
| `popt-devel` | Red Hat:hummingbird:1 | All versions | 0:1.19-11.2.hum1 |
| `popt-static` | Red Hat:hummingbird:1 | All versions | 0:1.19-11.2.hum1 |

## How do I fix CVE-2026-18839?

Apply the vendor's patch.

## Is CVE-2026-18839 being exploited?

There is no known exploitation of CVE-2026-18839 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18839 and fix it if it is affected.

What it is: CVE-2026-18839 is a low-severity vulnerability in Red Hat Enterprise Linux 10, published on 5 Aug 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-18839 in the wild and no public exploit code.

Affected product: Red Hat Enterprise Linux 10. 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-2026-18839/ (Markdown: https://insights.sbomify.com/CVE-2026-18839/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18839
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18839
- OSV: https://osv.dev/vulnerability/CVE-2026-18839

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18839/
Summaries are generated and may contain mistakes; the official description above is the record.