CVE-2026-22102: Webserver Arbitrary File Write Vulnerability

CVE-2026-22102 Overview

CVE-2026-22102 is an arbitrary file write vulnerability affecting a webserver endpoint that accepts POST requests. The endpoint processes the filename parameter from the HTTP Content-Disposition header without validation or sanitization. Attackers can supply crafted filenames containing path traversal sequences to write files to arbitrary locations on the target system. This weakness maps to [CWE-20: Improper Input Validation]. Exploitation enables two distinct impacts: denial of service through overwriting critical system files, and remote code execution by replacing shell scripts that later run through scheduled tasks, service invocations, or other execution paths. No authentication is required to reach the vulnerable endpoint.

Critical Impact
Unauthenticated network attackers can write arbitrary files to the host, leading to system-file corruption or remote code execution via overwritten shell scripts.

Affected Products

Specific affected products are not enumerated in the NVD entry. Refer to the DIVD Security Advisory for the current list of impacted vendors and versions.

Discovery Timeline

2026-07-13 - CVE-2026-22102 published to NVD
2026-07-13 - Last updated in NVD database

Technical Details for CVE-2026-22102

Vulnerability Analysis

The vulnerability exists in a webserver endpoint that handles multipart or file-upload style POST requests. The server extracts the filename attribute from the Content-Disposition request header and uses that value directly when writing the request body to disk. No canonicalization, allowlisting, or directory restriction is applied to the supplied path.

An attacker sends a POST request containing a Content-Disposition header where the filename value includes traversal sequences such as ../ or an absolute path. The server writes the attacker-controlled request body to that location, using the privileges of the webserver process.

The impact splits into two exploitation paths. Overwriting configuration files, binaries, or libraries can crash services and produce denial of service. Overwriting shell scripts, cron entries, or startup scripts converts the primitive into remote code execution once the modified script executes.

Root Cause

The root cause is improper input validation [CWE-20]. The webserver trusts a client-supplied header field as a filesystem path. Secure handling requires stripping directory components, enforcing a fixed upload directory, and rejecting paths containing traversal characters or absolute prefixes.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker sends a single crafted POST request with a malicious Content-Disposition: form-data; name="file"; filename="../../etc/cron.d/rootshell" header, or a similar payload targeting a script executed by the operating system. The request body becomes the new contents of the targeted file. Refer to the DIVD Security Advisory for endpoint specifics and payload structure.

Detection Methods for CVE-2026-22102

Indicators of Compromise

POST requests to the affected endpoint containing Content-Disposition headers with filename values that include ../, ..\, or absolute paths beginning with / or a drive letter.
Unexpected modifications to shell scripts, cron files, systemd units, or webserver-writable binaries with recent timestamps aligned to inbound HTTP traffic.
New or altered files owned by the webserver process user in directories outside its designated upload path.

Detection Strategies

Inspect web access logs and reverse-proxy logs for POST requests whose multipart payloads contain traversal sequences or suspicious filename attributes.
Deploy web application firewall rules that decode Content-Disposition values and block requests where the filename parameter contains path separators or traversal tokens.
Correlate file-integrity monitoring events on /etc, /usr/local/bin, /var/spool/cron, and application script directories with recent HTTP activity to the affected service.

Monitoring Recommendations

Enable file integrity monitoring on system directories and application script paths, with alerting on writes performed by the webserver service account.
Forward webserver, WAF, and host telemetry to a centralized analytics platform to correlate HTTP request patterns with filesystem changes.
Alert on process creation events where a shell interprets scripts recently modified by the webserver user identity.

How to Mitigate CVE-2026-22102

Immediate Actions Required

Restrict network access to the affected webserver endpoint using firewall rules or reverse-proxy allowlists until a patched version is deployed.
Run the webserver process under a least-privileged account that cannot write to system directories, cron paths, or executable scripts.
Audit filesystem locations writable by the webserver user for unexpected recent modifications and validate script contents against known-good baselines.

Patch Information

Consult the DIVD Security Advisory for the current list of affected vendors, fixed versions, and coordinated release information. Apply vendor-supplied patches as soon as they become available for your deployment.

Workarounds

Deploy a WAF or reverse-proxy rule that rejects POST requests where the Content-Dispositionfilename parameter contains /, \, .., or null bytes.
Mount the webserver working directory with noexec where feasible, and place cron and startup script directories on filesystems not writable by the webserver account.
Disable the affected upload endpoint at the reverse proxy if the functionality is not required for production operation.

bash

# Example nginx rule to block traversal in Content-Disposition filenames
location /vulnerable/endpoint {
    if ($http_content_disposition ~* "filename=\"?[^\"]*(\.\.|/|\\\\)") {
        return 403;
    }
    proxy_pass http://backend;
}