CriticalCVE-2018-0147

    Cisco Secure Access Control System Java Deserialization Vulnerability (CVE-2018-0147)

    Published In CISA KEV since Sources: CVE.org

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    What is affected, what to do

    A vulnerability in Java deserialization used by Cisco Secure Access Control System (ACS) prior to release 5.8 patch 9 could allow an unauthenticated, remote attacker to execute arbitrary commands on an affected device. The vulnerability is due to insecure deserialization of user-supplied content by the affected software.

    The vulnerability is being actively exploited; treat it as a priority. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Cisco Secure Access Control System eq Cisco Secure Access Control System..Cisco Secure Access Control System

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

    Metrics

    9.8

    Priority

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

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: CVE.org

    18.2 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 97.2

    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
    224.60 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
    9.8 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
    9.8
    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“.

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    18.2 %
    Elevated — model estimates 10-50% exploitation likelihood.
    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
    97.2
    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: total
    Source: CISA Vulnrichment, as of 8 November 2024
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-20

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The flaw is network-reachable without authentication, has low attack complexity, and lands the attacker directly as root on the central AAA system. That effectively hands over control of who may log into network infrastructure, plus harvestable credentials and shared secrets. Java deserialization is easy to weaponise with public gadget tooling, and exploitation likelihood is rated very high, although CISA does not flag known ransomware use. Typical targets are organisations with legacy Cisco estates still running the end-of-life ACS. If any ACS is reachable from user or external networks, treat it as critical and act immediately; even behind a strictly isolated management network, keep it high priority, since the end-of-life status forces migration regardless.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Locate every Cisco Secure Access Control System (ACS) instance, physical or virtual, and record its release. Every version prior to 5.8 patch 9 is affected (Cisco Bug ID CSCvh25988).
      • Patch: Upgrade to ACS 5.8 patch 9 or later. Older trains such as 5.2 or 5.x below 5.8 must first move to 5.8. Check the Cisco advisory for CSCvh25988 for the exact patch bundle.
      • Restrict exposure now: Lock down the ACS web/management interface (typically HTTPS/443) with ACLs or firewall rules so only a dedicated admin subnet or jump hosts can reach it. Remove any exposure to the internet or user VLANs.
      • Assume compromise if it was exposed: Successful exploitation yields root on your AAA server. If the box was reachable before patching, preserve its logs, review its outbound connections, and consider rebuilding from a clean image rather than patching in place.
      • Rotate secrets: On any suspicion of compromise, rotate the following:
        • RADIUS shared secrets and TACACS+ keys on all network access devices
        • the ACS AD/LDAP service account
        • local ACS admin accounts
        • any device enable passwords stored in ACS
      • Address lifecycle: Cisco ACS is end-of-life. Raise the migration to Cisco ISE, or an equivalent AAA platform, as an urgent change, because you should not expect further fixes for an unsupported product.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation:

        • Place ACS in a dedicated management segment.
        • Inbound, permit only RADIUS (UDP 1812/1813, optionally 1645/1646) and TACACS+ (TCP 49) from known NAD IPs, and management only from the admin subnet.
        • Outbound, apply default-deny: allow only AD/LDAP, DNS, NTP and syslog. This kills reverse shells and tool staging.

      • IPS/WAF rule: Block or alert on HTTP(S) requests to ACS whose bodies carry serialized Java objects:

        • magic bytes AC ED 00 05
        • Base64 prefix rO0AB
        • known gadget class strings such as org.apache.commons.collections, InvokerTransformer or ysoserial

        This requires TLS inspection in front of ACS, for example via a reverse proxy.

      • Admin access (IAM): Route all administrative access to ACS through PAM-brokered jump hosts with MFA. Allow no direct access from workstations.

      • Least privilege in the directory: Limit the ACS AD service account to read-only rights, with no Domain Admin or write permissions, to cap the blast radius if ACS is compromised.

      • Fallback authentication: Document local break-glass accounts on NADs so ACS can be isolated quickly without locking operations out of the network.

    3. Runbook step 3

      Detection rules

      • Network (Suricata/Zeek): Alert on serialized Java objects sent to ACS. Example: 
        alert http any any -> $ACS_SERVERS any (msg:"Java serialized object to Cisco ACS"; flow:to_server; http.request_body; content:"|AC ED 00 05|"; sid:1000001;)
        Add a companion match on rO0AB in headers or body.
      • ACS egress: Hunt Zeek conn.log or firewall logs for ACS connecting to non-approved destinations, especially the internet, odd ports or long-lived sessions. Example in SPL: 
        index=fw src_ip IN (acs_ips) NOT dest_ip IN (allowed_ips) | stats count by dest_ip, dest_port
      • Web/proxy logs: Watch for POST requests to ACS from outside the admin subnet, oversized request bodies with Content-Type: application/x-java-serialized-object, and bursts of HTTP 500 responses following POSTs.
      • ACS syslog/integrity: Alert on new local admin accounts, unexpected configuration changes, service restarts, and edits to NAD definitions or shared secrets. Forward these events to the SIEM and correlate them with the change calendar.
      • Downstream abuse on NADs: Review TACACS+/RADIUS accounting for admin logins to switches and routers that do not match a ticket. A compromised AAA server can approve arbitrary authentications.

    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

    A vulnerability in Java deserialization used by Cisco Secure Access Control System (ACS) prior to release 5.8 patch 9 could allow an unauthenticated, remote attacker to execute arbitrary commands on an affected device. The vulnerability is due to insecure deserialization of user-supplied content by the affected software. An attacker could exploit this vulnerability by sending a crafted serialized Java object. An exploit could allow the attacker to execute arbitrary commands on the device with root privileges. Cisco Bug IDs: CSCvh25988.

    Source: NVD (NIST), cvelistv5, CISA KEV Catalog

    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
    —Cisco Secure Access Control System
    • Cisco Secure Access Control System
    • —
    ciscosecure_access_control_system
    • 5.2\(0.3\)
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-20Improper Input Validation

      Class

      The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

      Entry at MITRE CWE-20

    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

    • securitytracker.com1040463Vulnerability database, x_refsource_SECTRACK, Third-party advisory, Vulnerability database
    • securityfocus.com103328Vulnerability database, x_refsource_BID, Broken link, Third-party advisory, Vulnerability database
    • tools.cisco.comsecurity/center/content/CiscoSecurityAdvisory/cisco-sa-20180307…x_refsource_CONFIRM, Vendor advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2018-0147government-resource, US government resource
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