What is the CVSS score of CVE-2025-26399?

CVE-2025-26399 has a CVSS 3.1 base score of 9.8 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 28.2%.

Is there a public PoC exploit available for CVE-2025-26399?

Yes, a public proof-of-concept exploit is available for CVE-2025-26399. Prioritise patching immediately. EPSS: 28.2%.

How to fix or mitigate CVE-2025-26399?

Within 24 hours: Identify all affected systems and apply vendor patches immediately. Restrict deserialization to trusted data sources and implement integrity checks.

Web Help Desk CVE-2025-26399

CRITICAL

Deserialization of Untrusted Data (CWE-502)

2025-09-23 psirt@solarwinds.com

RCE Deserialization Web Help Desk Solarwinds

9.8

CVSS 3.1 · NVD

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Vulnerability Assessment

Weakness	CWE CWE-502 OWASP Top 10:2025 A08:2025 - Software or Data Integrity Failures ASVS 5.0 V1 - Encoding and Sanitization Safe deserialization, type allowlists MITRE ATT&CK 2 techniques across 2 tactics: Execution, Initial Access The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Impact	Critical risk (CVSS 9.8). Three iterations of the same vulnerability class indicate systemic deserialization issues in Web Help Desk. Organizations that patched twice are still vulnerable.
Exploit ScenarioDerived	An attacker sends crafted serialized data to the AjaxProxy endpoint. The deserialization executes commands on the WHD server, providing access to all help desk tickets (which often contain sensitive information like credentials and system access details).

Act Now Prioritize within 24-48h. Why: In CISA KEV with patch available.

Exploited in the wild (CISA KEV) Patch available 28.2% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 28, 2026

SolarWinds Web Help Desk contains an unauthenticated deserialization RCE via AjaxProxy, a patch bypass of both CVE-2024-28988 and CVE-2024-28986, the third iteration of this vulnerability.

Earlier versions of this analysis (1)

v1 Mar 28, 2026 - 19:13 CVSS 9.8

The third deserialization RCE in SolarWinds Web Help Desk, bypassing patches for both CVE-2024-28988 and CVE-2024-28986. Unauthenticated attackers can execute commands through the AjaxProxy endpoint.

RemediationAI

Apply the latest SolarWinds patches. Consider the pattern of repeated bypasses when evaluating continued use of the product.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

The CWE-502 deserialization in AjaxProxy processes untrusted data without proper class filtering. This is a double patch bypass, indicating the remediation approach was fundamentally insufficient.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 9.8 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Patch released

Mar 28, 2026 - 19:13 nvd

Patch available

Added to CISA KEV

Mar 10, 2026 - 13:11 cisa

CISA KEV

CVE Published

Sep 23, 2025 - 05:15 nvd

CRITICAL 9.8

DescriptionNVD

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.

Executive ViewAI

Why It Matters

Organizations using SolarWinds Web Help Desk face critical risk from CVE-2025-26399, a insecure deserialization vulnerability rated CVSS 9.8. Insecure deserialization could allow attackers to execute arbitrary code by providing crafted serialized data. This vulnerability is actively exploited in the wild (KEV-listed) and requires immediate remediation. A patch is available and should be applied immediately given the critical severity.

Business Impact: Severe

Compensating Controls

Apply vendor patch. If immediate patching is not feasible: (1) Restrict deserialization endpoints; (2) Implement integrity checks on serialized data; (3) Use type-safe alternatives.

Threat Intelligence Overview

Threat Score

5.8/10

Composite threat intelligence

EPSS Score

28.2%

Top 4% exploitable

Exploit

POC

Public exploit code exists

Data Quality

6 sources

Confidence: High

NVD

CVE.org

CISA KEV

EPSS CERT-EU POC (1)

GitHub

VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity CRITICAL

CISA KEV Yes

Public POC Yes

EPSS 28.2%

Patch available Yes

Active threat Yes

Deciding rule

In CISA KEV with patch available

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Immediate

Exploitation· derived

Active

System Exposure· derived

Open

Automatable· derived

Yes

Human Impact

Very High

Priority Score

147

Low Medium High Critical

KEV: +50

EPSS: +28

CVSS: +49

PoC: +20

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Insecure Deserialization CRITICAL

Insecure deserialization occurs when an application converts serialized data (a stream of bytes representing an object's state) back into a living object without proper validation.

Remote Code Execution CRITICAL

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.