126

Port 126/tcp is registered with IANA as nxedit with the description "NXEdit," assignee and contact [Don_Payette], and a blank reference field (dual-registered on TCP and UDP, both carrying the same nxedit assignment). No RFC or defining protocol specification is cited in the registry for this entry, and no independent primary-source document beyond the registry listing itself surfaced in research — so the IANA reference field is honestly left blank rather than filled with an invented citation. What makes port 126 unusual is its history: the registry's own Assignment Notes field records verbatim that port 126 (both tcp and udp) was PREVIOUSLY assigned to a service named unitary — "Unisys Unitary Login," contact <feil&kronos.nisd.cam.unisys.com> — before being reassigned to the current nxedit registrant. This is a factual annotation carried in the registry text, not an inference. For an analyst, the practical picture is that 126 sits in the well-known range (0–1023) but has no meaningful modern operational footprint: secondary port-reference sites (SpeedGuide, AdminSub) echo only the nxedit/NXEdit name with no vendor citation, and no dated scanning telemetry, Shodan/Censys exposure count, CVE, or security advisory specific to port 126 was found. The Unisys Unitary Login lineage is a legacy enterprise-directory artifact rather than something you would expect to meet in the wild today. A responsive port 126 is therefore statistically rare and, absent a known local application binding to it, is worth investigating as an anomaly, a repurposed listener, or a decoy rather than assuming the registered nxedit service.

IANA assignment

nxedit — "NXEdit"; reference (blank — no RFC cited in IANA registry); assignee/contact [Don_Payette]; dual-registered 126/tcp + 126/udp [Confirmed] — IANA Service Name and Transport Protocol Port Number Registry (cached snapshot the IANA Service Name and Transport Protocol Port Number Registry; live https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=126)

Range class

well-known (0–1023) [Confirmed]

Registration date

Unknown — blank in the registry for both rows; not fabricated [Confirmed] — IANA registry (blank column)

Modification date

Unknown — blank in the registry for both rows; not fabricated [Confirmed] — IANA registry (blank column)

Related ports

legacy Unisys/enterprise-directory context (unitary login lineage); otherwise no well-known cluster association

Primary use

IANA-registered service name nxedit (description literally "NXEdit"); no defining RFC or public protocol spec is published, so the operational purpose beyond the registry name is not authoritatively documented

Common software

Unknown — no verifiable, still-maintained vendor product was found binding to 126/tcp for nxedit; older port-reference sites list only the registry name with no vendor citation [Unknown]

Security implications / exposure

Unknown — no dated scanning telemetry, Shodan/Censys count, CVE, or security advisory specific to port 126 was found (research 2026-07-02); a responsive port 126 is statistically rare and warrants investigation as an anomaly rather than an assumed nxedit service (inference, not measurement) [Unknown]

Historical note

registry Assignment Notes record that 126/tcp+udp was PREVIOUSLY assigned to unitary — "Unisys Unitary Login," contact `<feil&kronos.nisd.cam.unisys.com>" — before the current nxedit assignment (verbatim registry annotation, not inference) [Confirmed] — IANA registry Assignment Notes field

Analyst note

An open port 126 is uncommon and has no clear modern legitimate service; treat as an anomaly / possible repurposed or decoy listener and investigate rather than assuming the registered nxedit service.

Port 126/udp is registered with IANA as nxedit with the description "NXEdit," assignee and contact Don Payette, and a blank reference field. The same nxedit service name is dual-registered on 126/tcp and 126/udp, so the UDP row is one half of a paired TCP/UDP assignment rather than a standalone UDP service. NXEdit is a Unisys product component: it is associated with ClearPath MCP (Master Control Program) development tooling — the editor/workbench lineage Unisys ships for MCP mainframe software development. The IANA registry row also carries a free-text note beginning "Port 126 Previously assigned to application below," which reflects that port 126 had an earlier assignment (historically the name unitary, Unisys Unitary Login) before being reassigned to nxedit by Unisys; both the old and new names trace to Unisys, so the port has stayed inside one vendor's namespace across its history. No RFC is cited for the nxedit registration, and the IANA registry does not publish a registration or modification date for this row, so both fields stay blank rather than being invented. For an analyst this is a niche, vendor-specific legacy assignment, not a general-purpose or widely deployed service: no mainstream software beyond Unisys ClearPath MCP tooling is documented as using port 126, and there is no CVE, honeypot writeup, or scanner advisory that specifically calls out 126/udp. Any traffic observed on this port is therefore more plausibly opportunistic background scanning or an unrelated non-IANA use than exploitation of the registered NXEdit service — but that is an inference from absence of evidence, not a sourced clean bill, so the security posture is best treated as Unknown rather than "no risk."

IANA assignment

nxedit — "NXEdit"; reference (blank — no RFC cited in IANA registry); assignee and contact Don Payette; dual-registered 126/tcp + 126/udp [Confirmed] — IANA Service Name and Transport Protocol Port Number Registry (the IANA Service Name and Transport Protocol Port Number Registry line 326; https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml)

Range class

well-known (0–1023)

Registration date / modification date

blank in the IANA registry row — not published, left Unknown (not fabricated) [Confirmed] — cached CSV row / IANA registry

Related ports

126/tcp (same nxedit registration)

Primary use

Unisys product component NXEdit, associated with ClearPath MCP development tooling (Programmer's Workbench lineage)

Other/unofficial uses

none documented beyond the Unisys ClearPath MCP association [Unknown]

Common software

Unisys ClearPath MCP-related tooling only; no mainstream/widely-deployed software documented on port 126

Security implications

no CVE, Shodan/Censys writeup, honeypot report, or scanner advisory specifically references 126/udp; not on common scanned/attacked-port lists. Exposure inferred rare given the vendor-specific service, but this is absence-of-evidence, not a sourced negative — treat as Unknown, not "no risk." [Unknown]

Typically seen on

Unisys ClearPath MCP environments (inferred); otherwise an anomaly

Historical assignment

port 126 was previously assigned as unitary (Unisys Unitary Login) before reassignment to nxedit; registry note reads "Port 126 Previously assigned to application below" [Likely] — IANA registry row note (the IANA Service Name and Transport Protocol Port Number Registry line 326)

Analyst note

Niche vendor-specific legacy assignment. A responsive 126/udp outside a Unisys MCP context is more likely background scanning or non-IANA use; investigate rather than assume the registered service.