507

Port 507/tcp is registered with IANA under the bare service name "crs," but no RFC, vendor protocol specification, or actively deployed software has been found bound to it; as of an August 2026 search it reads as an essentially undocumented placeholder assignment rather than a live service, so it has no established legitimate use and should not be reachable from the public internet.

IANA's registry entry lists 507/tcp and 507/udp together under the identical service name "crs," with the description field simply repeating "crs" and no expanded name, RFC reference, or registration date recorded. The registration is credited to assignee Brad Wright, with no further confirmable detail beyond that name.

No authoritative source expands "crs" into a full protocol or product name. One web search synthesis rendered it as "Content Replication System," but this could not be traced to any citable primary document, so it is treated as unverified and not adopted as the entry's description.

The only community mention found is a 2018 Gentoo Forums thread whose title references "crs on tcp/udp 507," but its content could not be retrieved after two failed fetch attempts, and the title alone reads as a user parsing the IANA registry label rather than reporting a real application. No vendor documentation, blog post, or support thread ties a specific piece of software to this port.

nmap-services open-frequency data measures 507/tcp at 0.00005 (about 0.005% of scanned hosts) and 507/udp at 0.000593 (about 0.06%) — both low but genuine, sampled readings rather than an absence of data.

Exposure

No documented legitimate protocol runs on 507/tcp, so a responsive instance is unexplained and worth investigating rather than treated as routine service traffic.

Common software

No application or vendor software could be confirmed as generating traffic on this port as of an August 2026 search.

IANA assignment

crs — description field repeats "crs"; reference blank; assignee Brad_Wright; dual-registered 507/tcp + 507/udp [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry crs 507/tcp, crs 507/udp

Range class

well-known/system (0–1023) [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry crs 507/tcp

Prevalence

nmap-services open-frequency 507/tcp = 0.00005 (~0.005%); 507/udp = 0.000593 (~0.06%) [Confirmed] — this site's own tooling

Related ports

507/udp (twin dual registration under the same "crs" name)

Primary use

no documented, actively-used protocol found; registry entry is a placeholder with no RFC or spec

Other/unofficial uses

none confirmed; an unverifiable "Content Replication System" expansion surfaced in one web synthesis and is not adopted [Unknown]

Security implications

no CVE or malware association found as of an August 2026 search; auditmypc.com verdict "Virus/Trojan: No"

Typically seen on

no host or product type confirmed; a responsive port is anomalous given the lack of documented protocol [Unknown]

Analyst note

507/tcp has no confirmed legitimate service behind it — a responsive port is unusual and worth investigating rather than assumed benign.

Port 507/udp carries no documented protocol or known application; IANA's registry lists only the bare service name "crs" with no RFC reference, so there is no established software that legitimately listens here, and the port should be treated as internal-only or simply unused rather than assumed safe to expose to the public internet.

IANA's Service Name and Transport Protocol Port Number Registry assigns the name "crs" to both 507/tcp and 507/udp, attributed to assignee Brad Wright, with the Reference column left blank. No RFC, internet-draft, or other technical specification accompanies the entry, and the registry supplies no expansion of what "crs" stands for.

A search for real-world usage — vendor documentation, support forums, game or P2P client references, and port-lookup aggregator sites — turned up nothing specific to 507/udp. Several aggregator sites (SpeedGuide, adminsub.net, my-addr.com, portsmaster.net) were either unreachable or explicitly reported no known service for this port, so the absence of an application is treated as a sourced null result rather than a research gap.

Measured open-frequency from the nmap-services corpus is low: 507/udp shows approximately 0.06% and 507/tcp approximately 0.005%, consistent with a port that sees essentially no legitimate deployed traffic. Given the blank protocol specification and negligible observed usage, a responsive 507/udp is best read as an anomaly worth investigating rather than as expected infrastructure.

Exposure

No documented protocol or vendor application exists for 507/udp; treat any responsive host as anomalous and investigate rather than assume a legitimate service.

Prevalence

nmap-services open-frequency for 507/udp is approximately 0.06% (507/tcp approximately 0.005%), indicating the port is almost never found open in the wild.

Unverified claim

A general web-search summary suggested an "ONC RPC" association for this port, but no primary source (IANA reference, vendor documentation, or CVE record) corroborates it, so it is not reported as fact.

IANA assignment

crs — no description text; Reference column blank; assignee [Brad_Wright]; dual-registered 507/tcp + 507/udp [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry (crs 507/udp)

Range class

well-known (0–1023) [Confirmed]

Prevalence

nmap-services open-frequency 507/udp ≈ 0.000593 (~0.06%); 507/tcp ≈ 0.00005 (~0.005%) [Confirmed] — this site's own tooling

Related ports

507/tcp (same IANA "crs" dual registration)

Primary use

Unknown — no RFC or protocol specification is associated with the "crs" service name; IANA registry gives no descriptive text beyond the name itself

Other/unofficial uses

None found — no vendor documentation, forum thread, or application-specific reference located for 507/udp as of an August 2026 search [Unknown]

Security implications

no CVE, malware family, or scanning-campaign association verified as of an August 2026 search; essentially never seen open

Typically seen on

no known legitimate deployment; an open instance is anomalous [Likely]

Analyst note

507/udp has no documented protocol, application, or security history — a responsive host is statistically rare and should be treated as unidentified/anomalous traffic pending further investigation, not assumed to be a known service.