CriticalCVE-2025-20337

    Cisco ISE API Unauthenticated Remote Code Execution Vulnerability (CVE-2025-20337)

    Published In CISA KEV since Sources: pwn.watch, CERT-EU, CVE.org

    What is affected, what to do

    A vulnerability in a specific API of Cisco ISE and Cisco ISE-PIC could allow an unauthenticated, remote attacker to execute arbitrary code on the underlying operating system as root. The attacker does not require any valid credentials to exploit this vulnerability.

    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 Identity Services Engine Software eq 3.3.0..3.3.0
    • Cisco Identity Services Engine Software eq 3.3 Patch 2..3.3 Patch 2
    • Cisco Identity Services Engine Software eq 3.3 Patch 1..3.3 Patch 1
    • Cisco Identity Services Engine Software eq 3.3 Patch 3..3.3 Patch 3
    • Cisco Identity Services Engine Software eq 3.4.0..3.4.0
    • Cisco Identity Services Engine Software eq 3.3 Patch 4..3.3 Patch 4
    • Cisco Identity Services Engine Software eq 3.4 Patch 1..3.4 Patch 1
    • Cisco Identity Services Engine Software eq 3.3 Patch 5..3.3 Patch 5
    • Cisco Identity Services Engine Software eq 3.3 Patch 6..3.3 Patch 6
    • Cisco ISE Passive Identity Connector eq 3.2.0..3.2.0
    • Cisco ISE Passive Identity Connector eq 3.1.0..3.1.0
    • Cisco ISE Passive Identity Connector eq 3.3.0..3.3.0
    • Cisco ISE Passive Identity Connector eq 3.4.0..3.4.0

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

    Metrics

    10.0

    Priority

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

    Source: NVD, CVSS v3

    10.0

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: pwn.watch, CERT-EU, CVE.org

    74.5 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.49

    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
    239.09 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 exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
    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
    10.0 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
    10.0
    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
    74.5 %
    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
    99.49
    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 26 July 2025
    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-74

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This vulnerability is network-reachable without authentication or user interaction and grants root on a core security control. It currently ranks among the CVEs most likely to be exploited. ISE is the trust anchor for NAC, RADIUS/TACACS+ and AD integration, so a compromised node lets an attacker harvest credentials, rewrite network access policy and pivot into segmented OT or KRITIS zones. CISA has not flagged ransomware use, but the flaw is highly attractive for initial access. Treat any ISE instance whose API is reachable beyond a tightly controlled management network as critical and patch within 24 hours. Treat strictly isolated instances as high priority and patch within days.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Identify every Cisco ISE and ISE-PIC node (PAN, MnT, PSN, pxGrid) and confirm the exact release via show version or the admin GUI. Per the context, the affected releases are 3.3.0, 3.3 Patch 1–5, 3.4.0 and 3.4 Patch 1.
      • Patch: A fix is available from the vendor; look up the fixed release in the Cisco Security Advisory for CVE-2025-20337. Prioritise API-reachable nodes, then roll out across the whole deployment. Applying only part of the hotfix set does not close this issue, so verify that the installed patch level explicitly covers CVE-2025-20337.
      • Restrict API reachability now: ACL or firewall the management and API interfaces (typically TCP 443 and, if enabled, the ERS API on TCP 9060) so only dedicated admin jump hosts can reach them. Cut any exposure to the internet or user VLANs immediately.
      • Disable unused APIs: Turn off ERS and OpenAPI under Administration > Settings > API Settings unless an integration (MDM, SOAR, ticketing) strictly requires them.
      • Triage for compromise before patching: Preserve the config backup, support bundle and MnT logs. Patching does not remove persistence an attacker has already planted. If indicators exist, treat the node as fully compromised, because the attacker had root.
      • Rotate secrets on suspicion: Rotate the AD join account, the RADIUS/TACACS+ shared secrets on all network access devices, pxGrid certificates, ERS API credentials and local admin passwords.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Place ISE management and APIs in a dedicated management VLAN. From NAD networks, allow only RADIUS (UDP 1812/1813) and TACACS+ (TCP 49), plus guest and BYOD portals on their designated ports. Default-deny admin and API ports from every other zone.
      • Egress filtering: Limit outbound traffic from ISE nodes to what they need: AD/LDAP, DNS, NTP, syslog, Cisco update servers and configured integrations. Drop and log everything else. This blocks reverse shells and tool staging after RCE.
      • IPS/WAF: On upstream Firepower or Snort 3, enable the current Talos signatures for the 2025 Cisco ISE RCE vulnerabilities in blocking mode. Where a reverse proxy fronts the API, add a rule that rejects requests containing shell metacharacters (;, |, `, $() or oversized JSON bodies.
      • IAM and least privilege: Restrict API accounts to "ERS Operator" (read-only) wherever write access isn't required. Give each integration its own account so you can rotate credentials surgically.
      • Operational resilience: Prepare NAD fallback before you rebuild a node, such as a critical-auth VLAN or local break-glass accounts. This matters most in KRITIS environments, where a NAC outage disrupts operations.

    3. Runbook step 3

      Detection rules

      • ISE logs (MnT/syslog): Look for API calls from unauthorised source IPs, bursts of HTTP 500 or error responses on API endpoints, and requests with no preceding successful admin authentication. SPL example: index=ise sourcetype=cisco:ise:syslog (ERS OR api) NOT src_ip IN (<jump_hosts>) | stats count by src_ip, uri
      • Network telemetry (Zeek/Suricata/NetFlow): Alert on any new outbound connection from ISE nodes to external or unknown destinations, especially on unusual ports or with long-lived sessions (a reverse-shell pattern). KQL example: CommonSecurityLog | where SourceIP in (ise_nodes) and DestinationIP !in (allowlist) | summarize count() by DestinationIP, DestinationPort
      • Firewall and proxy logs: Review hits on ISE ports 443 and 9060 from user, guest or internet zones. Once the ACLs are hardened, a single hit warrants investigation.
      • On-node integrity: Work with Cisco TAC on root-level or forensic checks. Look for unknown processes, new cron jobs, modified SSH authorized_keys, and recently timestamped files in /tmp or /opt. Also review the ISE admin audit logs for newly created admin or API accounts.
      • Downstream indicators: Watch for unexpected ISE policy changes (authorization profiles, exception rules) and for the AD join account authenticating from non-ISE hosts (Windows Event ID 4624/4768).

    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 a specific API of Cisco ISE and Cisco ISE-PIC could allow an unauthenticated, remote attacker to execute arbitrary code on the underlying operating system as root. The attacker does not require any valid credentials to exploit this vulnerability. This vulnerability is due to insufficient validation of user-supplied input. An attacker could exploit this vulnerability by submitting a crafted API request. A successful exploit could allow the attacker to obtain root privileges on an affected device.

    Source: pwn.watch, certeu_advisory, cvelistv5, NVD (NIST), 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
    CiscoCisco Identity Services Engine Software
    • 3.3.0
    • 3.3 Patch 5
    • 3.3 Patch 2
    • 3.4.0
    • 3.3 Patch 4
    • 3.3 Patch 6
    • 3.3 Patch 3
    • 3.4 Patch 1
    • 3.3 Patch 1
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    CiscoCisco ISE Passive Identity Connector
    • 3.2.0
    • 3.1.0
    • 3.3.0
    • 3.4.0
    • —
    • —
    • —
    • —
    ciscoidentity_services_engine
    • 3.3.0
    • 3.4.0
    • —
    • —
    ciscoidentity_services_engine_passive_identity_connector
    • 3.3.0
    • 3.4.0
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

      Class

      The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.

      Entry at MITRE CWE-74

    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

    • sec.cloudapps.cisco.comcisco-sa-ise-unauth-rce-ZAd2GnJ6Vendor advisory, pwn-watch
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2025-20337government-resource, US government resource
    • pwn.watchpwn.watch: Cisco Identity Services Engine: 2 exploited vulnerabilities (CVE-2025-20281, CVE-2025-20337)pwn-watch
    • NVD (NIST)NVD: CVE-2025-20281pwn-watch
    • NVD (NIST)NVD: CVE-2025-20337pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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