CVE-2026-55418

Received Received - Intake

FastGPT S3 Object Access Vulnerability via Unauthorized Key Handling

Publication date: 2026-07-07

Last updated on: 2026-07-07

Assigner: GitHub, Inc.

Description

FastGPT is an open source AI knowledge base platform. Prior to v4.15.0-beta5, two FastGPT file handlers authorize an unrelated resource and then sign or read an S3 object using a key taken directly from the request, without checking that the key belongs to the caller's team. Because S3 object keys are global within the bucket and carry the tenant id only as a path segment, an attacker can supply another team's key and obtain its file contents through the chat-file presign endpoint or dataset preview endpoint. This issue is fixed in version v4.15.0-beta5.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-07-07

Last Modified

2026-07-07

Generated

2026-07-08

AI Q&A

2026-07-08

EPSS Evaluated

N/A

NVD

CVE-2026-55418

Affected Vendors & Products

Vendor	Product	Version / Range
fastgpt	fastgpt	to 4.15.0-beta5 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-639	The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.

Attack-Flow Graph

Executive Summary

This vulnerability exists in FastGPT, an open source AI knowledge base platform, prior to version v4.15.0-beta5. Two file handlers in FastGPT authorize access to an unrelated resource and then sign or read an S3 object using a key taken directly from the request without verifying that the key belongs to the caller's team.

Since S3 object keys are global within the bucket and only include the tenant ID as a path segment, an attacker can supply another team's key and access that team's file contents through specific endpoints such as the chat-file presign endpoint or the dataset preview endpoint.

This issue was fixed in version v4.15.0-beta5.

Impact Analysis

An attacker exploiting this vulnerability can access files belonging to other teams by supplying their S3 object keys, potentially exposing sensitive or confidential information.

Because the vulnerability allows unauthorized read access to data, it can lead to data breaches and compromise confidentiality.

The CVSS score of 8.6 (high severity) indicates a significant risk due to the vulnerability being remotely exploitable without privileges or user interaction.

Mitigation Strategies

To mitigate this vulnerability, upgrade FastGPT to version v4.15.0-beta5 or later, where the issue has been fixed.

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