CriticalCVE-2025-26399

    SolarWinds Web Help Desk Deserialization of Untrusted Data Privilege Escalation Vulnerability (CVE-2025-26399)

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

    What is affected, what to do

    The vulnerability CVE-2025-26399 allows an attacker to execute remote code on SolarWinds Web Help Desk without authentication, granting full control over the host machine. It is actively exploited in ransomware campaigns and is listed in the CISA KEV catalog. All versions without the specific patch for CVE-2024-28988 and originally CVE-2024-28986 are affected. An immediate update to the latest version is urgently required to mitigate this vulnerability.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. 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
    • SolarWinds Web Help Desk eq 12.8.7 and below..12.8.7 and below

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

    90.1 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.80

    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
    264.82 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
    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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    90.1 %
    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.

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    99.80
    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
    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-502

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is the third patch bypass of a WHD deserialisation chain and CISA flags it as actively used in ransomware campaigns — a clear sign that automated exploit tooling exists. The vector is network-reachable without authentication and without user interaction; success yields immediate code execution as the WHD service account, typically followed by lateral movement into the ticketing and asset database. Internet-exposed WHD instances at MSPs, IT service providers and help desks adjacent to critical infrastructure are the canonical target profile. For any affected organisation CVE-2025-26399 is a P0 patch item for this week; instances that cannot be patched belong behind an authenticating reverse proxy or offline until the fix is in place.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Upgrade SolarWinds Web Help Desk (WHD) to 12.8.7 Hotfix 1 or later — this is the current fix for the AjaxProxy deserialisation path; versions up to and including 12.8.6 are vulnerable. Pull the hotfix from the SolarWinds Customer Portal and apply per the vendor advisory (back up the whd database and whd/conf directory first).
      • If the patch cannot be deployed immediately, pull the WHD instance off the public internet. Set reverse-proxy / load-balancer / firewall rules so the management URLs (TCP 8081/8443 or the configured listener) are only reachable from the internal admin VLAN.
      • Hard-block the URL path /helpdesk/WebObjects/Helpdesk.woa/ws/AjaxProxy and any generic /AjaxProxy routes at the upstream reverse proxy or WAF (HTTP 403) until the hotfix is verified active. This endpoint is the attack surface and is not needed by external users in normal operation.
      • Run a compromise assessment: inspect whd/logs/whd.log, whd/logs/catalina.out and the OS process tree for unexpected children of the Tomcat/WHD service (java.exe → cmd.exe/powershell.exe or java → /bin/sh), covering the window since July 2024 given the predecessor CVEs CVE-2024-28986 / CVE-2024-28988.
      • Rotate the WHD service-account credential plus LDAP/AD integration credentials and API tokens if the instance was exposed or shows indicators. Review the backend database credentials (PostgreSQL/MSSQL) as well.
      • Open an incident ticket at raised priority (KEV plus known-ransomware-use flag) and put IR on standby.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: WHD belongs in a management segment; ingress only on 443 from the designated user VLAN, no direct internet ingress. Mandate VPN or ZTNA fronting for external technicians.
      • Host egress filtering: restrict outbound traffic from the WHD host to the strict minimum (SMTP relay, LDAP, DB, SolarWinds update endpoint). Block arbitrary outbound HTTP(S), DNS to unapproved resolvers, LDAP/SMB into other segments — this breaks second-stage download and C2.
      • WAF rule: alert and block POST/PUT requests to AjaxProxy paths that carry Java-serialised payload markers (magic bytes ac ed 00 05, Base64 prefix rO0AB, or Content-Type application/x-java-serialized-object).
      • Endpoint hardening: run the Tomcat/WHD service under a dedicated unprivileged account (not SYSTEM, not root). Use AppLocker / WDAC or SELinux policy to forbid the Java process from spawning shells, script interpreters or LOLBins (certutil, bitsadmin, mshta, curl, wget).
      • IAM: enforce strong passphrases / MFA on local WHD admin accounts, remove any defaults. Keep the LDAP service account read-only with minimal scope.
      • Backup and recovery: ensure a current offline copy of WHD configuration and database exists (ransomware flag), and rehearse the restore path.

    3. Runbook step 3

      Detection rules

      • EDR / Sysmon EID 1 process ancestry: ParentImage ends with java.exe or tomcat*.exe and Image ∈ (cmd.exe, powershell.exe, wscript.exe, cscript.exe, rundll32.exe, mshta.exe, bitsadmin.exe, certutil.exe) — high-fidelity signal for deserialisation RCE. Linux equivalent via auditd: execve where ppid is a Java/Tomcat process and comm ∈ (sh, bash, nc, curl, wget, python).
      • Web-server access logs (Tomcat localhost_access_log): POSTs to URI patterns *AjaxProxy* with unusually large bodies (> 2 KB) or anomalous user agents. KQL shape: W3CIISLog | where csUriStem contains "AjaxProxy" and csMethod == "POST" and scStatus in (200,500) and csBytes > 2000.
      • Network telemetry (Zeek/Suricata): HTTP POST bodies containing ysoserial-typical class strings (CommonsCollections, BeanComparator, TemplatesImpl, Runtime.exec). Suricata rule shape: alert http any any -> $WHD_SERVERS any (msg:"WHD AjaxProxy Java deser"; content:"AjaxProxy"; http_uri; content:"|ac ed 00 05|"; http_client_body; sid:1000026399;).
      • Sysmon EID 11 / 15 or auditd path: new files under the WHD webroot (whd/bin/webapps/, whd/conf/) or the Tomcat work directory with extensions .jsp, .war, .class outside planned deployment windows.
      • SIEM correlation: HTTP 5xx spike on the WHD endpoint followed within 60 s by the Java process initiating outbound connections to non-allowlisted destinations or DNS lookups with high entropy.

    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

    SolarWinds Web Help Desk was found to be susceptible to an unauthenticated AjaxProxy deserialization remote code execution vulnerability that, if exploited, would allow an attacker to run commands on the host machine. This vulnerability is a patch bypass of CVE-2024-28988, which in turn is a patch bypass of CVE-2024-28986.

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

    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
    SolarWindsWeb Help Desk
    • 12.8.7 and below
    • —
    solarwindsweb_help_desk
    • 12.8.7
    • ≤ 12.8.6
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-502Deserialization of Untrusted Data

      Base

      The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.

      Entry at MITRE CWE-502

    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

    • solarwinds.comSolarWinds Web Help Desk — CVE-2025-26399pwn-watch
    • documentation.solarwinds.comen/success_center/whd/content/release_notes/whd_12-8-7-hotfix-1…
    • microsoft.comen-us/security/blog/2026/02/06/active-exploitation-solarwinds-w…Third-party advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2025-26399government-resource
    • pwn.watchpwn.watch: SolarWinds Web Help Desk: SolarWinds Web Help Desk Deserialization of Untrusted Data Vulnerabilitypwn-watch
    • NVD (NIST)NVD: CVE-2025-26399pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch

    Reanalysis & status changes

    Chronological NVD audit events for this CVE — reanalyses, CVSS updates, CPE diffs.

    1. CVE Translatednvd@nist.gov

      • Translation: after Title: Web Help Desk de SolarWinds, Description: SolarWinds Web Help Desk se encontró que era susceptible a una vulnerabilidad de ejecución remota de código por deserialización de AjaxProxy no autenticada que, si se explotaba, permitiría a un atacante ejecutar comandos en la máquina anfitriona. Esta vulnerabilidad es un bypass de parche de CVE-2024-28988, que a su vez es un bypass de parche de CVE-2024-28986.
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