551
Summary
- // typical exposure
- Restricted (trusted networks only) — The port's official cybercash assignment is defunct with no current public-facing purpose, and its one confirmed modern reuse (Oracle Corente gateway-to-Control-Point authentication) is designed for firewalled, trusted-network connections rather than open internet exposure.
- // common applications
- CyberCash payment protocol (historical, Oracle Corente Cloud Services Exchange Traffic on this port is most often absent or incidental scan noise given the defunct original cybercash assignment; Oracle's Corente Cloud Services Exchange documentation has reported using TCP 551 for gateway-to-Control-Point authentication traffic.
- // analyst note
- An open 551/tcp is rare (0 sampled open-frequency on TCP) and its official purpose is defunct; confirm against Oracle Corente gateway usage before treating an unexpected listener as suspicious.
- // if you see it open
- No CVE is recorded in the NVD as of an August 2026 search, and no malware/trojan family is associated with this port on AuditMyPC as of the same search. The one confirmed modern use (Oracle Corente gateway authentication) expects firewalled, trusted-network connections rather than public exposure; SANS ISC shows only routine, low-volume scan monitoring with no notable activity.
About port 551/tcp.
Port 551/tcp carries the IANA-registered service cybercash, tied to the defunct 1990s CyberCash Inc. electronic-payment protocol, and it should stay off the public internet. No live payment traffic tied to that original purpose exists today, so the assignment is effectively a vacant legacy name that one modern vendor has reused informally for an unrelated, firewalled purpose.
IANA registers 551 as cybercash on both TCP and UDP, assignee Donald E. Eastlake, with the registry's reference field populated as RFC 1898. CyberCash Inc. built one of the earliest internet credit-card payment gateways in the 1990s before ceasing operations in the early 2000s, and the port name is one of its remaining traces in the registry.
Beyond the official name, the one solid modern sighting is Oracle's Corente Cloud Services Exchange documentation, which instructs administrators to forward or open TCP 551 to terminate authenticated connections between Corente Services Gateways, IPSec clients, and the Corente Services Control Point when a customer's own firewall sits in front of the gateway.
A secondary port-database aggregator also lists an unnamed "DeviceShare" application against TCP 551, but no primary vendor source corroborates it, so it is treated here as unverified rather than fact. SANS ISC tracks the port under routine scan monitoring without notable volume, and no CVE or malware family is recorded against it as of an August 2026 search.
- Exposure
- Official cybercash assignment is defunct with no live public-facing purpose; the one confirmed modern reuse (Oracle Corente gateway authentication) expects firewalled, trusted-network connections, not open exposure.
- Notable CVE
- No CVE is recorded in the NVD as of an August 2026 search; the SANS ISC port-551 page's CVE Links section was empty.
- Malware/Trojan association
- Not listed as malware-associated as of an August 2026 search — AuditMyPC's port-551 page carries its standard disclaimer above a de facto negative verdict.
- Scanning activity
- SANS Internet Storm Center tracks port 551 under routine port monitoring; no populated scan-volume figures or comments were shown at check time, consistent with a low-activity port.
- IANA assignment
cybercash— description "cybercash"; assignee [Donald_E_Eastlake]; reference [RFC1898]; dual-registered 551/tcp + 551/udp [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry cybercash 551/tcp- Range class
- well-known/system (0–1023) [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry cybercash 551/tcp
- Prevalence
- nmap-services open-frequency 551/tcp = 0 (sampled, not observed open); 551/udp ≈ 0.000774 [Confirmed] — this site's own tooling
- Related ports
- other legacy 1990s payment-service assignments in the system/well-known range [Unknown — no specific cluster identified this pass]
Primary use
historical CyberCash Inc. electronic-payment protocol (registry reference RFC 1898); effectively defunct today, with no observed live traffic tied to the original purpose
Other/unofficial uses
Oracle Corente Cloud Services Exchange gateway-to-Control-Point authentication, a vendor-documented reuse of the legacy port
Security implications
no CVE recorded and no malware association found as of an August 2026 search; the one confirmed legitimate modern use is designed for firewalled, trusted-network connections only
Typically seen on
Oracle Corente Cloud Services Exchange gateway deployments; otherwise rare/incidental as a largely vacant legacy assignment
- Analyst note
- An open 551/tcp is rare (0 sampled open-frequency on TCP) and its official purpose is defunct; confirm against Oracle Corente gateway usage before treating an unexpected listener as suspicious.
About port 551/udp.
Port 551/udp is IANA-registered to cybercash, the defunct 1990s CyberCash payment protocol (RFC 1898); it carries no known legitimate traffic today, so it should be treated as anomalous rather than expected on any network, public or private.
The registration dates to RFC 1898 (Donald E. Eastlake, "CyberCash Credit Card Protocol Version 0.8," February 1996, Informational), which defined a mechanism for transmitting credit-card payment data over the Internet. Port 551 is dual-registered on both TCP and UDP to the same cybercash service, with the IANA registry listing Eastlake as both assignee and contact and no registration or modification date recorded.
CyberCash Inc., the company behind the protocol, was founded in 1994 and filed for bankruptcy in March 2001 following a security breach and Y2K-related billing problems. Its wallet-based payment approach was superseded by SSL/TLS-based e-commerce, and the IANA assignment was never withdrawn even though the underlying protocol and its client/server software are defunct.
As of an August 2026 search, no actively maintained software, CVE, or named malware/trojan is documented as using 551/udp. The nmap-services open-frequency for 551/udp is 0.000774 (about 0.077%), while 551/tcp is recorded at exactly 0 — a sampled reading, not an absence.
- Exposure
- Anomalous — CyberCash has been defunct since its 2001 bankruptcy, and no maintained software is known to listen on 551/udp today, so open or active traffic here is unusual and worth investigating.
- Historical protocol
- RFC 1898 defined the CyberCash Credit Card Protocol for transmitting payment data; the assignment was never withdrawn after the company folded.
- Malware/CVE
- No CVE or named trojan/malware is documented as associated with 551/udp as of an August 2026 search.
- Dual registration
- 551 is registered to the same
cybercashservice on both TCP and UDP, so findings for one transport largely carry over to the other.
- IANA assignment
cybercash— description "cybercash"; reference RFC 1898; assignee Donald E. Eastlake; dual-registered 551/tcp + 551/udp [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry cybercash 551/udp- Range class
- system/well-known (0–1023) [Confirmed]
- Prevalence
- nmap-services open-frequency 551/udp = 0.000774 (~0.077%); 551/tcp = 0 (sampled, not observed open) [Confirmed] — this site's own tooling
- Related ports
- 551/tcp (same
cybercashregistration)
Primary use
CyberCash Credit Card Protocol Version 0.8 (RFC 1898, Feb 1996) — transmitting payment/credit-card data over the Internet; protocol is defunct
Other/unofficial uses
none documented; no modern application is confirmed to use this port
Security implications
essentially never legitimately open today; CyberCash Inc. bankrupt since March 2001; no documented CVE or malware association
Typically seen on
legacy/historical CyberCash deployments (effectively none remaining); otherwise an anomaly [Likely]
- Analyst note
- An active 551/udp is statistically rare and tied to a protocol whose operating company has been defunct since 2001 — treat unexpected traffic as worth investigating rather than routine.
Service assignments.
| Name | Protocol | Description | Open frequency |
|---|---|---|---|
| cybercash | UDP | — | 0.08% |
| cybercash | TCP | — | 0.00% |
Service assignments from the IANA Service Name and Transport Protocol Port Number Registry, with open-frequency data from nmap-services.