# CVE-2026-81856: Terminal escape sequence injection in Hex via unneutralized server-supplied output

> A malicious package publisher can inject terminal escape sequences to forge displayed URLs, hide output, or write to the clipboard in Hex.

- **Severity:** Low 2.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 12 Oct 2026
- **Updated:** 16 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-81856, EEF-CVE-2026-81856, GHSA-fpmj-3cxg-p766, UBUNTU-CVE-2026-81856

## What is CVE-2026-81856?

CVE-2026-81856 is a low-severity vulnerability in hexpm hex, published on 12 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Improper Neutralization of Escape, Meta, or Control Sequences vulnerability in hexpm hex allows a malicious package publisher or a hostile repository server to inject terminal control sequences into the output of Mix tasks.

Hex prints strings supplied by the package repository and the documentation search service straight to the terminal through Hex.Shell.info/1 and Hex.Shell.error/1, neutralizing no control characters. Affected sinks span package metadata and configuration snippets in mix hex.info, search results in mix hex.package search and mix hex.search, owner and organization listings, publish and sponsor URLs, the authenticated username in mix hex.user, policy identities in mix hex.policy, and API error bodies rendered by Hex.Utils.print_error_result/1. A malicious package can embed ANSI escape sequences (cursor movement, line erase, carriage returns, OSC 52 clipboard writes) or Unicode bidirectional overrides in any of those fields, so the bytes reach the terminal unchanged, forging displayed URLs, package descriptions and suggested commands, concealing real output, or writing to the clipboard. No authentication or privileged position is required; only publishing a package.

This issue affects hex: from 0.0.1 before 2.5.2.

Weakness: CWE-150 (Improper Neutralization of Escape, Meta, or Control Sequences)

## Which versions are affected by CVE-2026-81856?


## How do I fix CVE-2026-81856?

Upgrade to a fixed version.

## Is CVE-2026-81856 being exploited?

There is no known exploitation of CVE-2026-81856 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81856 and fix it if it is affected.

What it is: CVE-2026-81856 is a low-severity vulnerability in hexpm hex, published on 12 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-81856 in the wild and no public exploit code.

Affected product: hexpm hex. 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-2026-81856/ (Markdown: https://insights.sbomify.com/CVE-2026-81856/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81856
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81856
- OSV: https://osv.dev/vulnerability/CVE-2026-81856

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81856/
Summaries are generated and may contain mistakes; the official description above is the record.