CVE-2026-23537: Feast Feature Server RCE Vulnerability

CVE-2026-23537 Overview

CVE-2026-23537 is a missing authorization vulnerability [CWE-862] in the Feast Feature Server's /save-document endpoint. The endpoint permits unauthenticated remote attackers to write arbitrary JSON files to the server's filesystem. Path restrictions intended to constrain write locations can be bypassed, allowing attackers to overwrite application configurations or startup scripts. Any attacker with network reachability to the server can exploit this flaw without credentials or user interaction. Successful exploitation can result in unauthorized system modifications, denial of service through disk exhaustion, or remote code execution when overwritten files are subsequently executed by the host.

Critical Impact
Unauthenticated network attackers can overwrite configuration and startup files on Feast Feature Server hosts, enabling code execution and service disruption.

Affected Products

Feast Feature Server (Feast open-source feature store)
Red Hat Data Services distributions bundling Feast
Deployments exposing the /save-document endpoint on reachable networks

Discovery Timeline

2026-07-01 - CVE-2026-23537 published to NVD
2026-07-02 - Last updated in NVD database

Technical Details for CVE-2026-23537

Vulnerability Analysis

The Feast Feature Server exposes a /save-document HTTP endpoint that accepts JSON payloads and writes them to the server's local filesystem. The endpoint does not enforce authentication or authorization checks before performing the write operation. This matches the pattern described by CWE-862, Missing Authorization.

The server implements filesystem restrictions intended to confine writes to a designated storage directory. These controls do not fully normalize or validate the supplied file path. Attackers can construct requests that escape the intended directory and target arbitrary locations on the host.

The attack requires only network access to the exposed endpoint. No credentials, tokens, or prior session state are needed. The Red Hat advisory and the GitHub Pull Request for Feast contain the code-level fix and additional detail.

Root Cause

The root cause is the combination of an unauthenticated write endpoint and insufficient path validation. The endpoint trusts client-supplied filename or path components when constructing the destination on disk. Path traversal sequences and absolute paths are not consistently rejected before the write occurs.

Attack Vector

An attacker sends an HTTP request to the /save-document endpoint on a reachable Feast Feature Server. The request body contains JSON content and a filename or path parameter crafted to escape the intended directory. The server writes the attacker-controlled JSON to a sensitive location such as an application configuration file, a systemd unit, or a Python startup module. On subsequent process restart or scheduled task execution, the overwritten file is loaded, resulting in remote code execution or service failure. Repeated writes can also exhaust disk capacity and cause denial of service.

No verified proof-of-concept code has been published. Refer to the Red Hat CVE Advisory and the Red Hat Bug Report for authoritative technical detail.

Detection Methods for CVE-2026-23537

Indicators of Compromise

HTTP POST requests to /save-document originating from unexpected source addresses or over public networks.
Request payloads containing path traversal sequences such as ../ or absolute paths in filename fields.
Unexpected modification timestamps on configuration files, startup scripts, or Python site-packages under the Feast service account.
New or modified JSON files outside the designated Feast document storage directory.

Detection Strategies

Inspect web access logs and reverse proxy logs for requests to /save-document, correlating client IP, request size, and response status.
Deploy file integrity monitoring on Feast configuration directories, service unit files, and application startup paths.
Alert on process launches by the Feast service account that spawn shells, interpreters, or network utilities shortly after a /save-document request.

Monitoring Recommendations

Forward Feast Feature Server access logs and host telemetry to a centralized analytics pipeline for correlation.
Baseline normal /save-document request volumes and alert on deviations in rate, source geography, or payload characteristics.
Monitor disk utilization on Feast hosts to detect write-based denial of service attempts.

How to Mitigate CVE-2026-23537

Immediate Actions Required

Restrict network access to the Feast Feature Server so only trusted clients can reach the HTTP interface.
Block or filter requests to /save-document at the reverse proxy or ingress layer until a patched version is deployed.
Audit the Feast host filesystem for unexpected JSON files and recently modified configuration or startup scripts.

Patch Information

Apply the upstream fix referenced in the GitHub Pull Request for Feast. Consult the Red Hat VEX Document for authoritative product state and fixed-version information for Red Hat distributions.

Workarounds

Place the Feast Feature Server behind an authenticating reverse proxy that requires client authentication for all endpoints.
Run the Feast process under a low-privilege service account with a read-only filesystem for configuration and startup directories.
Deny egress and cross-directory writes using mandatory access controls such as SELinux or AppArmor profiles scoped to the Feast document directory.

bash

# Configuration example: block /save-document at nginx until patched
location = /save-document {
    deny all;
    return 403;
}