Security readout for executives and security teams
Plain-English summary
This finding flags that a legacy "daytime" network service is running on a system. Daytime simply returns the current date and time to anyone who connects, but it exposes an unnecessary listening port that attackers can use to fingerprint the host or, in older setups, help amplify network floods. It is not a code vulnerability so much as an obsolete service that should be turned off on modern systems.
Executive priority
Low priority housekeeping. Address during routine hardening or the next maintenance window; no evidence of active exploitation, but leaving obsolete services enabled adds unnecessary attack surface and can lower audit and scanner ratings.
Technical view
CVE-1999-0638 records the presence of the daytime service (TCP/UDP port 13, RFC 867) on a host. The service returns a human-readable timestamp to any client that connects. Because it accepts unauthenticated requests and reflects data, it has historically been abused for reconnaissance and, when paired with other simple UDP services, for reflection or "ping-pong" traffic. The CVE record includes no CVSS score, CWE mapping, vendor, or affected product because it describes an exposed service rather than a specific software flaw.
Likely exposure
Any host with inetd/xinetd or an equivalent legacy service manager that still enables the daytime service on port 13/TCP or 13/UDP, particularly older Unix, Linux, or network appliance systems reachable from untrusted networks.
Exploitation context
Not listed in CISA KEV and no known active exploitation campaigns are cited in the source bundle. The condition is primarily a hygiene and attack-surface issue: it aids fingerprinting and can be misused in reflection-style traffic when other legacy UDP services are also open. No exploit code, payload, or offensive procedure is provided here.
Researcher notes
This is an "exposure" style CVE from the original 1999 batch rather than a software defect, which is why severity, CVSS, CWE, and affected products are all unspecified in the record. Treat detections as configuration findings: verify the listener, confirm whether it is inetd/xinetd/systemd-managed, and check for co-resident chargen or echo services that could compound the risk. Evidence in the bundle is limited to the CVE record itself.
Mitigation direction
- Disable the daytime service in inetd/xinetd or the OS service manager on affected hosts.
- Block TCP and UDP port 13 at the network perimeter and on host firewalls.
- Remove or disable other legacy simple services (echo, chargen, discard) at the same time.
- Confirm current vendor guidance before touching production appliances that may depend on legacy ports.
Validation and detection
- Run an authorized port scan against the host to confirm port 13/TCP and 13/UDP no longer respond.
- Review inetd.conf, xinetd.d, or systemd unit files to confirm the daytime service is disabled and masked.
- Check firewall and ACL rules to verify port 13 is blocked inbound from untrusted zones.
- Re-scan from an external vantage point after changes to confirm the exposure is closed.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
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CVE-1999-0638 mapping review
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Open ATT&CK lookup- Severity
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS and timeline data
No CVSS vectors or timeline events were available in the normalized CVE source material.
Source materials
- CVE List V5 sourceCVE List V5
- https://www.cve.org/CVERecord?id=CVE-1999-0638CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.