What is CVE-2026-81856?

CVE-2026-81856 is Terminal escape sequence injection in Hex via unneutralized server-supplied output. The supplied enrichment data classifies it as Unclassified mapped to CWE-150 CWE-150.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Active exploitation is not confirmed from current sources for CVE-2026-81856. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

No. CVE-2026-81856 is not listed in CISA KEV in the supplied enrichment data. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

Is there a public exploit?

1 public PoC repositories reported; 0 marked weaponized in current dataset. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with web/proxy/WAF logs, application logs, network IDS/IPS where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-81856 using CVSS 2.3, EPSS 0%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

Workarounds are not confirmed from current sources. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Prioritize based on EPSS, PoC availability, and external exposure. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

lowpublic exploit

CVE-2026-81856

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

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.

Published Oct 12, 2026Updated Oct 12, 2026Sources: NVD, hexpm (CNA), GitHub, Red Hat (VEX), SOCRadar CTI

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Exploit code

public exploit, none observed

EPSS

ahead of 0% of scored CVEs

Affects

hexpm

2 products listed

CVSS base

2.3

low · 2 sources

Remediation

The vendor's own words where we have them.

Upgrade Hex to 2.5.2 or later, for example with mix local.hex. Hex then escapes terminal control characters in text from hex.pm and the registry before printing it, and rejects registry dependencies whose package or repository name isn't a valid name.

Red Hat VEX · CVE-2026-81856

fixed0affected0not affected1

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Prioritize based on EPSS, PoC availability, and external exposure.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
hexpm	hex	0.0.1 to < 2.5.2	Vulnerable
hexpm	hex	211303e3f68f5d3ce06450c1ff1a7a770a9ab236	Vulnerable

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Scope

Attack Complexity

Low

Attack Vector

Network

Privileges Req

None

User Interaction

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
2.3	CVSS 4.0	low	—	—	hexpm (CNA)
4.3	CVSS 3.1	medium	—	—	Red Hat (VEX)

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

What this weakness leads to

MITRE's own consequences and mitigations for the weakness class — the authority's wording, not guidance derived from the CVSS vector.

MITRE

CWE-150 · Improper Neutralization of Escape, Meta, or Control Sequences

Unexpected State::

Mitigation: Developers should anticipate that escape, meta and control characters/sequences will be injected/removed/manipulated in the input vectors of their software system. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system.

Weakness & attack patterns

CWE-150

Attack patterns reported against this CVE. The ATT&CK techniques below are inferred from its weakness class.

CAPEC-81 · Web Logs TamperingCAPEC-41 · Using Meta-characters in E-mail Headers to Inject Malicious PayloadsCAPEC-93 · Log Injection-Tampering-ForgingCAPEC-134 · Email Injection

Public exploit

Capability, not use: code existing is a different claim from anyone running it.

Repositories

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Search application, proxy, and WAF logs for requests touching /1.
Prioritize edge telemetry for network-reachable hex.
Monitor for scanner or exploit-pattern traffic after 1 public PoC repositories were reported.

web/proxy/WAF logsapplication logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added · CVSS 3.1 2.3 (AV:N)
Oct 12, 2026 · NVD
Initial · CVE published
Oct 12, 2026 · NVD
CVE published by MITRE.
Oct 12, 2026 · SOCRadar CTI

References

7 on the record

cna.erlef.org/cves/CVE-2026-81856.html
Vendor Advisory, Mitre, NIST
github.com/hexpm/hex/commit/211303e3f68f5d3ce06450c1ff1a7a770a9ab236
Exploit, Third Party Advisory, Mitre, NIST
github.com/hexpm/hex/commit/dd3305ddf0032f6d0b468fd40dbbc3072bfcb8b8
Exploit, Third Party Advisory, Mitre, NIST
github.com/hexpm/hex/security/advisories/GHSA-fpmj-3cxg-p766
Exploit, Third Party Advisory, Mitre, NIST
osv.dev/vulnerability/EEF-CVE-2026-81856
Vendor Advisory, Mitre, NIST
access.redhat.com/security/cve/CVE-2026-81856
Vendor Advisory
www.cve.org/CVERecord?id=CVE-2026-81856
Vendor Advisory

Elsewhere on this site

hexpmevery CVE for this vendor
Unclassifiedsame class
CWE-150other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2026-81856 is Terminal escape sequence injection in Hex via unneutralized server-supplied output, a low vulnerability affecting hex from hexpm. The current evidence does not list it in CISA KEV, and the exploit status is: Active exploitation is not confirmed from current sources for CVE-2026-81856. Public exploit evidence is: 1 public PoC repositories reported; 0 marked weaponized in current dataset. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 2.3 describes technical severity, while EPSS 0% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.