# Terminal escape sequence injection in Hex via unneutralized server-supplied output

CVE record · `CVE-2026-81856`

- **Identifiers:** `CVE-2026-81856`
- **State:** Confirmed
- **Severity:** CVSS 2.3 Low
- **Critical:** No
- **CNA:** EEF
- **Weakness (CWE):** [CWE-150](https://cwe.mitre.org/data/definitions/150.html)
- **Tags:** [CWE-150](https://agentprime.io/advisories/tag/cwe-150.md)
- **Technologies:** [hex](https://agentprime.io/advisories/technology/hex.md)
- **Published:** 12 Oct 2026
- **Updated:** 16 Oct 2026
- **Reviewed by a person:** No

Published by the CVE Program (CNA: EEF) at 12 Oct 2026, 15:46 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it.

## Affected products, as the CNA wrote them

- Vendor: hexpm. Product: hex.
  - affected: `0.0.1 to before 2.5.2` (semver)
  - Other versions: unaffected
  - Package name: `hex`
  - purl: `pkg:otp/hex?repository_url=https:%2F%2Fgithub.com%2Fhexpm%2Fhex&vcs_url=repository_url=git%2Bhttps:%2F%2Fgithub.com%2Fhexpm%2Fhex.git`
- Vendor: hexpm. Product: hex.
  - affected: `211303e3f68f5d3ce06450c1ff1a7a770a9ab236 to before dd3305ddf0032f6d0b468fd40dbbc3072bfcb8b8` (git)
  - Other versions: unaffected
  - Package name: `hexpm/hex`
  - Collection: `https://github.com`
  - purl: `pkg:github/hexpm/hex`

## Not analysed yet

We haven’t published our own analysis of this CVE. If a person reviews it, this page will say what’s affected and what has to be true for it to matter.

## Severity and exploitation

- 2.3 Low, CVSS 4.0: `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`, from CNA (EEF)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0040, the 34th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

This record came from the full history of the CVE Program, published 12 Oct 2026. New records show when each source confirmed them.

## Sources

- [CVE List: CVE-2026-81856](https://www.cve.org/CVERecord?id=CVE-2026-81856)
- [NVD: CVE-2026-81856](https://nvd.nist.gov/vuln/detail/CVE-2026-81856)

### References from the CNA

- <https://github.com/hexpm/hex/security/advisories/GHSA-fpmj-3cxg-p766> (related, vendor-advisory)
- <https://cna.erlef.org/cves/CVE-2026-81856.html> (related)
- <https://osv.dev/vulnerability/EEF-CVE-2026-81856> (related)
- <https://github.com/hexpm/hex/commit/211303e3f68f5d3ce06450c1ff1a7a770a9ab236> (related)
- <https://github.com/hexpm/hex/commit/dd3305ddf0032f6d0b468fd40dbbc3072bfcb8b8> (patch)

Facts on this page come from the CVE List as the CNA published them, with CVSS from the sources named above, CISA KEV and FIRST EPSS. Vendors, products and versions are shown as the CNA wrote them. We don’t reproduce the CVE’s description.

## Check whether this affects you

This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it. Compare the affected versions above with what you run.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), `get_advisory` returns this record and `search_advisories` finds related ones. Setup: <https://agentprime.io/mcp.md>
- As JSON: <https://api.agentprime.io/v1/advisories/CVE-2026-81856>
- Everything that needs attention now: <https://agentprime.io/advisories/critical.md>

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The web page: <https://agentprime.io/advisories/CVE-2026-81856/>. Everything for agents: <https://agentprime.io/llms.txt>.