CVE-2025-26399 is a deserialization of untrusted data vulnerability in SolarWinds Web Help Desk. CISA added it to the Known Exploited Vulnerabilities catalogue on 9 March 2026, which means attackers have used it in real attacks. SolarWinds Web Help Desk contain a deserialization of untrusted data vulnerability in AjaxProxy that could allow an attacker to run commands on the host machine.
What the vulnerability means in a deserialization sink
Deserialization flaws are dangerous because they let untrusted input influence object state before normal validation or authorization checks can intervene. In a web help desk product, that can turn a routine request path into an execution path if the application trusts attacker-controlled serialized data.
The core issue is not just malformed input, but unsafe reconstruction of data into live application objects. When the deserialization routine can be reached by a remote user, the attacker may be able to trigger server-side behaviour that the application never intended to expose.
Why this class of flaw is high impact in help desk software
Help desk platforms often sit close to authentication, password reset, ticketing, and administrative workflows, which makes them valuable targets even when the vulnerability sits in a secondary component. If command execution is reachable, the effect can extend well beyond the help desk interface into the underlying host, adjacent services, and stored data.
That is why exploited help desk flaws are often treated as enterprise compromise risks rather than isolated application bugs. A successful exploit can create a foothold for follow-on actions such as credential theft, web shell deployment, service manipulation, or lateral movement.
For broader context on how exploit chains are prioritised and verified, compare the vulnerability against the NIST National Vulnerability Database record and the CVE Program entry, which are the authoritative references for the identifier itself.
How organisations assess exposure and reduce risk
Exposure assessment starts with an accurate asset inventory: where SolarWinds Web Help Desk is deployed, whether it is internet-facing, and whether the vulnerable AjaxProxy path is reachable from untrusted networks. Vendor advisories should be reviewed directly so teams can confirm scope, version information, and any workaround or patch guidance.
If immediate remediation is not possible, compensating controls should narrow exposure as much as practical. That usually means restricting network reachability, limiting administrative access, tightening reverse-proxy and WAF rules where they are effective, and watching for unexpected requests to the affected application path.
For a structured remediation workflow, Vulnerability Management Guide is the most relevant internal reference for scoping, prioritisation, and verification.
Detection, compromise review, and identity impact after exploitation
Because this vulnerability can lead to host-level command execution, defenders should review logs and telemetry for evidence of unusual process creation, unexpected child processes from the web application, suspicious outbound connections, and any post-exploit changes to the server. If exploitation is suspected, the review should also extend to persistence mechanisms and any access obtained through the host.
The identity impact can be material even when the initial issue is not an authentication bug. If attackers executed commands on the server, they may have accessed secrets, session material, configuration files, or service credentials stored on or reachable from the host. Those materials should be treated as potentially exposed and rotated or invalidated as appropriate.
That post-compromise review should include adjacent identity controls and recovery workflows, because exposed credentials often become the real blast radius after the initial exploit.
Risk and Threat Considerations
This vulnerability matters because a deserialization sink can convert a normal request into remote command execution on an exposed server. In practice, that means an attacker does not need to win a complex authentication battle if the vulnerable code path is reachable and the application trusts attacker-controlled input.
Failure mechanism: Unsafe deserialization reconstructs attacker-supplied data into application objects, which can trigger unintended methods or execution paths and hand control of the host to the attacker.
Impact: Successful exploitation can lead to full server compromise, data exposure, service disruption, and secondary compromise of credentials or secrets stored on the system.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
NIST CSF 2.0, NIST SP 800-53 Rev 5 and CIS Controls v8 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST CSF 2.0 | ID.AM-01 — Physical devices and systems within the organization are inventoried | Exposure assessment depends on knowing where the vulnerable product is deployed. |
| Recommendation — Inventory affected Web Help Desk assets and confirm whether any instance is internet-facing. | ||
| NIST SP 800-53 Rev 5 | RA-5 — Vulnerability Monitoring and Scanning | The term describes a publicly exploited vulnerability that requires active assessment and verification. |
| SI-10 — Information Input Validation | Deserialization of untrusted data is an input-handling failure that this control category addresses. | |
| Recommendation — Scan for the vulnerable application path and verify remediation status on every instance. Validate and constrain external input before it reaches deserialization logic. | ||
| CIS Controls v8 | CIS-7 — Continuous Vulnerability Management | Exploited CVEs require continuous identification, prioritisation, and remediation. |
| CIS-13 — Network Monitoring and Defense | Post-exploit detection relies on monitoring for suspicious application and host activity. | |
| Recommendation — Prioritise the affected product in your vulnerability management queue and track remediation to closure. Monitor for unusual server-side processes, connections, and access patterns tied to the vulnerable host. | ||
Practitioner Guidance
What to watch for: Prioritise this issue on any internet-exposed Web Help Desk deployment, especially where the product supports sensitive administrative or recovery workflows. If you cannot patch immediately, assume the reachable surface is under active scrutiny and tighten access aggressively.
Practitioner takeaway: Treat confirmed exploitation or strong suspicion of exploitation as a host compromise event, not just an application patching task.
Related resources from NHI Mgmt Group
- CVE-2024-28987 (SolarWinds Web Help Desk Hardcoded Credential)
- CVE-2026-20131 (Cisco Secure Firewall Management Center (FMC) Software and Cisco Security Cloud Control (SCC) Firewall Management Deserialization of Untrusted Data)
- CVE-2021-23758 (Ajax.NET Professional Deserialization of Untrusted Data)
- CVE-2023-21529 (Microsoft Exchange Server Deserialization of Untrusted Data)