External risk intelligence

Arbitrary File Write Vulnerability in Web Server Endpoint

CVE advisorySeverity: CRITICAL (CVSS 9.3)

CVE-2026-22102

The vulnerability exists in a web server endpoint that processes incoming POST requests. Because the flaw involves handling HTTP headers to write files, it is commonly exposed in web applications or internet-facing services that accept file uploads or interact with user-supplied request data, making it likely to be reachable from the internet in standard deployments.

Denial of Service

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability has been identified in a web server endpoint that allows an attacker to write to arbitrary file locations by sending a specially crafted POST request. This could potentially lead to a denial of service by corrupting system files or enable remote code execution if critical scripts are overwritten.

Unrestricted file writing via web requests.
Critical systems could be impacted.
Confirm if your web applications are affected.

Attack Path

How an attacker could exploit the issue

An attacker can exploit this vulnerability by sending a crafted POST request to a specific web server endpoint. This endpoint improperly handles a filename parameter within the Content-Disposition header, allowing the attacker to specify arbitrary file locations for writing. This capability could be used to disrupt services by overwriting critical system files or to achieve remote code execution by replacing executable scripts, which could then be triggered through other means.

No authentication or user interaction needed.
POST request to specific web server endpoint.
Denial of service or code execution.

Live Threat

Current exploitation, exposure, and threat context

A POST request to a specific web server endpoint could be used to write to arbitrary file locations. This occurs when the endpoint accepts a filename from the Content-Disposition header without proper validation, potentially leading to denial of service by overwriting system files or remote-code execution if shell scripts are overwritten and subsequently triggered.

System files and execution scripts.
Via unvalidated filename in a POST request.
Denial of service or remote code execution.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability affects web server endpoints and could be exploited by external actors to overwrite arbitrary files. Infrastructure and platform teams, alongside network/security teams, are likely responsible for identifying and mitigating this risk. The first practical step is to locate all instances of the affected technology, assess their exposure and business criticality, and then plan remediation based on the identified risk.

Ownership: Infrastructure and Platform Teams.
Verify first: Reachable instances and business criticality.
Action: Plan remediation based on risk.

Supplementary metadata

CVSS vector

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Frequently asked questions

What is the web server component affected by CVE-2026-22102?

This CVE concerns a web server endpoint that processes incoming POST requests. It acts as a gateway for handling data uploads or interactions. The vulnerability lies in how the server processes the Content-Disposition header, which is typically used in web communications to define how files are handled when transmitted between a client and a server.

How would you describe the vulnerability in CVE-2026-22102?

This vulnerability is an Improper Input Validation issue, classified as CWE-20. In plain terms, the server blindly trusts the filename provided by the user in a network request without checking if the location is authorized. Because it fails to validate this input, the server can be tricked into writing or overwriting files anywhere on the system that the application has permission to access.

What triggers this file write vulnerability?

An attacker triggers this by sending a specially crafted POST request containing a malicious filename within the Content-Disposition header. Crucially, the vulnerability does not require authentication or user interaction to activate. It only triggers when the specific web server endpoint receives the malformed header; requests that do not include this specific parameter or target different endpoints remain unaffected.

Why should I be concerned about CVE-2026-22102?

You should care if you manage web applications that handle POST requests. According to Halo Surface Signal, this vulnerability is likely to be reachable from the internet in standard deployments because it resides in a web server endpoint. If your service is internet-facing, it is at higher risk of being reached by unauthorized actors compared to services restricted to an internal network.

How do I start responding to this CVE?

Begin by identifying all servers running the affected software within your infrastructure. Once identified, evaluate which instances are exposed to the internet and assess the business criticality of those systems. Prioritize these high-risk areas for remediation, such as restricting access to the affected endpoint or applying vendor updates as they become available to ensure input validation is properly enforced.

References

csirt.divd.nl/DIVD-2026-00001/

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.