CriticalCVE-2023-29552

    Service Location Protocol (SLP) Denial-of-Service Vulnerability (CVE-2023-29552)

    Published In CISA KEV since Sources: SingCERT, pwn.watch, CVE.org

    What is affected, what to do

    The Service Location Protocol (SLP, RFC 2608) allows an unauthenticated, remote attacker to register arbitrary services. This could allow the attacker to use spoofed UDP traffic to conduct a denial-of-service attack with a significant amplification factor.

    The vulnerability is being actively exploited; treat it as a priority. Update VMware ESXi to version 7.0. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • SUSE Linux Enterprise Server eq 11..11
    • SUSE Linux Enterprise Server eq 12..12
    • SUSE Linux Enterprise Server eq 15..15
    • VMware ESXi lt *..7.0
    Fixed in
    • VMware ESXi 7.0

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    7.5

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: SingCERT, pwn.watch, CVE.org

    64.0 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.22

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    218.83 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploited
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    7.5 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.5
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    64.0 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.22
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CISA assessment (SSVC)
    Exploitation: active · automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 28 January 2025

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The flaw is network-reachable without authentication and impacts availability only, but its exceptionally large amplification factor makes it a favoured vector for volumetric reflection DDoS; exploitation likelihood is very high, while CISA reports no known ransomware use. The core risk is less about losing your own data and more about your infrastructure being weaponised against third parties, saturating your own bandwidth and upstream links — for NIS2 entities a reportable and reputation-damaging scenario. Treat any internet-exposed SLP service (typically ESXi hosts, SLES servers, storage management) as a 24-hour fix; internal-only SLP can follow the regular patch cycle provided anti-spoofing and segmentation are in place.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Map external exposure: Scan all internet-facing ranges for open 427/UDP and 427/TCP (SLP), e.g. nmap -sU -sT -p 427 <public ranges>, or query Shodan/Censys for your own address space. Every hit is a candidate reflector for DDoS against third parties.
      • Block port 427 at the perimeter: Drop inbound 427/UDP+TCP at edge firewalls, cloud security groups and upstream ACLs. SLP is a LAN discovery protocol with no legitimate internet use case.
      • Disable SLP where not required: SUSE Linux Enterprise Server 11/12/15 and SUSE Manager Server: systemctl disable --now slpd, remove openslp-server if unused. VMware ESXi (the largest reflector population, not listed in the context but widely affected): /etc/init.d/slpd stop, esxcli network firewall ruleset set -r CIMSLP -e 0, chkconfig slpd off.
      • Apply vendor fixes: SUSE has shipped updated openslp packages — look up the exact version in the SUSE security advisory for CVE-2023-29552. NetApp SMI-S Provider: patch available from the vendor — check the vendor advisory for the fixed version or mitigation.
      • Inventory other SLP speakers: Printers, BMC/IPMI controllers, storage management software and appliances often enable SLP by default; capture them in the CMDB via internal scans on 427.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Permit SLP only inside dedicated management VLANs; block inter-VLAN 427 traffic via ACL.
      • Anti-spoofing (BCP 38/84): Enable uRPF at network edges and egress-filter foreign source addresses so compromised internal hosts cannot launch spoofed requests.
      • IPS rule against external registration: The SLPv2 header starts with version byte 0x02 followed by the function ID (0x03 = SrvReg). Suricata idea: alert udp $EXTERNAL_NET any -> $HOME_NET 427 (msg:"SLPv2 SrvReg from external – CVE-2023-29552"; content:"|02 03|"; offset:0; depth:2; sid:9002955201; rev:1;). Add thresholded variants for function IDs 0x01 (SrvRqst), 0x06 (AttrRqst) and 0x09 (SrvTypeRqst) from external sources.
      • Rate limiting: Drop or throttle outbound UDP with source port 427 at the edge; pre-arrange ISP scrubbing and Flowspec filters for 427/UDP.
      • Host hardening: On SLES, firewall-cmd --permanent --remove-service=slp or an iptables rule dropping -p udp --dport 427 from untrusted sources; add "slpd disabled" to your CIS-based configuration baseline.

    3. Runbook step 3

      Detection rules

      • Zeek conn.log: Inbound flows to 427 from external networks: id.resp_p == 427 and not local_orig. Red flag: high resp_bytes/orig_bytes ratio fanned out to many distinct destination IPs.
      • NetFlow/firewall logs (KQL): CommonSecurityLog | where SourcePort == 427 and Protocol == "UDP" and DestinationIP !startswith "10." | summarize bytes=sum(SentBytes), dst=dcount(DestinationIP) by SourceIP, bin(TimeGenerated, 5m) | where bytes > 50000000 — flags active reflector abuse.
      • Suricata/IDS: SrvReg packets (function ID 0x03) from an external source followed by SrvTypeRqst/AttrRqst bursts — the typical staging step to inflate reply size.
      • Host telemetry (Linux): auditd/EDR alert on slpd execution where it should be disabled (auditctl -w /usr/sbin/slpd -p x -k slpd_exec); periodic compliance check ss -ulpn | grep :427.
      • External notifications: Route Shadowserver/national CERT "Open SLP" reports into SOC ticketing as a detection source.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    The Service Location Protocol (SLP, RFC 2608) allows an unauthenticated, remote attacker to register arbitrary services. This could allow the attacker to use spoofed UDP traffic to conduct a denial-of-service attack with a significant amplification factor.

    Source: CSA/SingCERT, pwn.watch, NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    netappsmi-s_provider
    • —
    • —
    service_location_protocol_projectservice_location_protocol
    • —
    • —
    susemanager_server
    • —
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxsuselinux_enterprise_server11
    Linuxsuselinux_enterprise_server12
    Linuxsuselinux_enterprise_server15
    Othervmwareesxi—

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited

    References & sources

    • datatracker.ietf.orgdoc/html/rfc2608Technical description
    • bitsight.comblog/new-high-severity-vulnerability-cve-2023-29552-discovered-…Exploit, Third-party advisory
    • blogs.vmware.comsecurity/2023/04/vmware-response-to-cve-2023-29552-reflective-d…Third-party advisory
    • cisa.govnews-events/alerts/2023/04/25/abuse-service-location-protocol-m…Third-party advisory, US government resource
    • suse.comsupport/kb/doc/?id=000021051Third-party advisory
    • curesec.comblog/article/CVE-2023-29552-Service-Location-Protocol-Denial-of…Exploit, Third-party advisory
    • github.comcuresec/slploadProduct
    • security.netapp.comadvisory/ntap-20230426-0001Third-party advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2023-29552government-resource, US government resource
    • pwn.watchpwn.watch: IETF Service Location Protocol (SLP): Denial-of-Service (CVE-2023-29552)pwn-watch
    • NVD (NIST)NVD: CVE-2023-29552pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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