501

Port 501/tcp carries the IANA-registered service stmf (STMF); it is an obscure, rarely-observed service that should stay off the public internet rather than be exposed, since no evidence supports a public-facing deployment pattern for it.

IANA lists 501/tcp and 501/udp under the service name stmf, with the description field reading literally "STMF" and no reference (RFC) cited. The registry's assignee and contact are both recorded as Alan Ungar, and no registration or modification date is present in the registry row.

IANA itself does not expand the STMF abbreviation. Several independent third-party port-lookup sites gloss it as "Simple Transportation Management Framework," tying it to the ITS (intelligent transportation systems) standard NTCIP 1101, used for data exchange with traffic signals, dynamic message signs, and roadside/environmental sensor controllers. This expansion is a secondary-source reading, not an IANA fact, so it is tagged Likely rather than Confirmed.

A separate aggregator snippet claimed STMF once meant "SET Transport Management Facility" tied to Secure Electronic Transaction (SET) credit-card processing, but no primary source substantiates this and it could not be verified independently, so it is recorded as Unknown rather than asserted.

Measured against the repo's port-data corpus (built from nmap-services), 501/tcp has an open-frequency of 0.000063 (~0.0063%) and 501/udp has 0.001186 (~0.12%); both are low, meaning a responsive port 501 is rare in general internet scanning.

IANA assignment

stmf — "STMF"; reference (blank — no RFC cited in IANA registry); assignee Alan Ungar; dual-registered 501/tcp + 501/udp [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry stmf 501/tcp

Range class

well-known (0–1023) [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry stmf 501/tcp

Prevalence

nmap-services open-frequency 501/tcp = 0.000063 (~0.0063%); 501/udp = 0.001186 (~0.12%) [Confirmed] — this site's own tooling

Related ports

no directly related-service cluster identified in this research pass; contrast the well-known system-services range (0–1023) generally

Primary use

unclear from IANA text alone; secondary sources gloss STMF as "Simple Transportation Management Framework" (NTCIP 1101, intelligent transportation systems)

Other/unofficial uses

an unverified aggregator claim of "SET Transport Management Facility" for SET credit-card processing could not be substantiated against any primary source [Unknown]

Security implications

no CVE or malware association found as of August 2026; obscure/rarely-open service; if the ITS/NTCIP linkage holds, legitimate traffic belongs on isolated control-system networks

Typically seen on

unclear; possibly intelligent-transportation-system roadside controllers or traffic management center software per the NTCIP 1101 gloss (not vendor-confirmed) [Unknown]

Analyst note

STMF is a low-prevalence, thinly documented registered service; treat an open 501/tcp as worth investigating rather than routine, and do not assume the NTCIP/transportation-framework reading without vendor confirmation.

Port 501/udp is IANA-registered under the service name stmf ("STMF"), but no authoritative document defines what runs on it, so a confident answer on public-internet exposure is not possible; the safest default is to keep it off the public internet like any other undocumented System Port.

The IANA registry lists the assignee as Alan Ungar (contact at farradyne.com), a blank Reference/RFC field, and identical dual registration on 501/tcp and 501/udp. No RFC or IANA-linked specification could be located to expand the acronym or describe the protocol.

Third-party port-lookup sites disagree on what STMF means. One cluster of aggregator pages ties it to "Simple Transportation Management Framework" under NTCIP 1101, an intelligent-transportation-systems (traffic-signal control) standard; a separate, less common claim links it to a "SET Transport Management Facility" for Secure Electronic Transaction credit-card processing. Neither is corroborated by the IANA registry, and the assignee's Farradyne Systems background (an ITS engineering firm) only lends circumstantial weight to the transportation reading. The port does not appear in Wikipedia's curated TCP/UDP port list, consistent with it being obscure and rarely encountered.

No specific software product could be confirmed as generating 501/udp traffic — only generic aggregator pages restating the IANA name turned up. No malware or CVE association was found as of an August 2026 search.

IANA assignment

stmf — "STMF"; reference (blank — no RFC cited in IANA registry); assignee Alan Ungar (registry handle [Alan_Ungar]; organisation domain farradyne.com); dual-registered 501/tcp + 501/udp [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry stmf 501/udp

Range class

well-known/System Port (0–1023) [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry stmf 501/udp

Prevalence

nmap-services open-frequency 501/udp ≈ 0.001186 (~0.12%); 501/tcp ≈ 0.000063 [Confirmed] — this site's own tooling

Related ports

500/udp (ISAKMP/IKE) and 502 (Modbus) are the immediate registry neighbors, though no functional relationship to stmf is established

Primary use

registered as stmf, but no authoritative specification or RFC could be located to describe the actual protocol behavior

Other/unofficial uses

third-party sites offer two conflicting, uncorroborated acronym expansions — "Simple Transportation Management Framework" (NTCIP 1101 intelligent transportation systems) and "SET Transport Management Facility" (credit-card SET processing)

Security implications

no CVE or malware association found as of an August 2026 search; auditmypc.com's port-class verdict reads "Virus/Trojan: No"

Typically seen on

not established; port is absent from Wikipedia's curated TCP/UDP port list, suggesting low real-world notability

Analyst note

Treat a responsive 501/udp host as an unusual/uncommon finding to investigate rather than a recognized service — no authoritative source confirms what should be running there.