CVE-2026-116685
Description
A flaw was found in the Model Context Protocol (MCP) Python SDK. When handling HTTP redirects, client connections follow redirects to different origins while improperly forwarding caller-supplied credential headers and request bodies. A remote attacker capable of influencing a trusted server's redirect destination could exploit this issue to intercept sensitive credentials and request payloads.
Statement
This vulnerability is rated as having a Moderate severity for Red Hat products because successful exploitation requires an adversary to manipulate or compromise the redirect responses of a trusted endpoint, representing a complex attack scenario. Within Red Hat environments utilizing Model Context Protocol client integrations over HTTP or SSE transports, exposure is limited to custom headers and request payloads, whereas standard authorization bearer tokens are discarded on cross-origin redirects. Deployments utilizing stdio-based MCP communications, as well as standalone MCP server implementations, remain unaffected by this flaw.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | N/A | 5.9 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | None | N/A | None |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Files or Directories; Read Memory; Read Application Data
Sensitive data may be exposed to attackers.
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