CVE-2026-55604 (GCVE-0-2026-55604)

Vulnerability from cvelistv5 – Published: 2026-07-09 21:13 – Updated: 2026-07-10 14:42

Title

@arikusi/deepseek-mcp-server has an Authorization Bypass Through User-Controlled Key

Summary

DeepSeek MCP Server is an MCP server for DeepSeek V4. Starting in version 1.4.2 and prior to version 1.7.0, the process-global `SessionStore` accepts caller-supplied `session_id` values without binding them to any authenticated principal or transport session. An attacker can enumerate active session IDs via `deepseek_sessions`, then reuse a victim-controlled `session_id` in `deepseek_chat` to retrieve and continue the victim's conversation context. Version 1.7.0 contains a patch.

Severity

8.6 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-07-10 14:40 UTC

CWE

CWE-639 - Authorization Bypass Through User-Controlled Key

Assigner

GitHub_M mitre root

References

2 references

URL	Tags
https://github.com/arikusi/deepseek-mcp-server/se…	x_refsource_CONFIRM
https://github.com/arikusi/deepseek-mcp-server/re…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
arikusi	deepseek-mcp-server	Affected: >= 1.4.2, < 1.7.0	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-55604

Vulnerability from fkie_nvd - Published: 2026-07-09 22:17 - Updated: 2026-07-10 19:20

Severity

8.6 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/arikusi/deepseek-mcp-server/releases/tag/v1.7.0
	security-advisories@github.com	https://github.com/arikusi/deepseek-mcp-server/security/advisories/GHSA-fh3r-g96v-f578
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/arikusi/deepseek-mcp-server/security/advisories/GHSA-fh3r-g96v-f578

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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      "affectedData": [
        {
          "product": "deepseek-mcp-server",
          "vendor": "arikusi",
          "versions": [
            {
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GHSA-FH3R-G96V-F578

Vulnerability from github – Published: 2026-08-25 18:37 – Updated: 2026-08-25 18:37

Summary

@arikusi/deepseek-mcp-server has an Authorization Bypass Through User-Controlled Key

Details

Cross-Session Data Exposure via Caller-Controlled `session_id`

Project / Repository: arikusi/deepseek-mcp-server
Affected version / commit tested: 1.6.0 / 04f28be2c6e99d3d4e443a6ae37cc35f0a71554a
Vulnerability type: Authorization bypass / cross-session data exposure Authentication required: No

Summary

The process-global SessionStore accepts caller-supplied session_id values without binding them to any authenticated principal or transport session. An attacker can enumerate active session IDs via deepseek_sessions, then reuse a victim-controlled session_id in deepseek_chat to retrieve and continue the victim's conversation context.

Affected Code

src/session.ts:42 - caller-controlled session IDs are looked up directly from the global in-memory map.
src/session.ts:67 - a new session is stored under the caller-controlled ID without ownership binding.
src/session.ts:109 - getMessages() retrieves messages for any supplied session ID.
src/tools/deepseek-chat.ts:195 - deepseek_chat creates or reuses the supplied session_id.
src/tools/deepseek-chat.ts:197 - previous messages are loaded from the supplied session_id.
src/tools/deepseek-chat.ts:198 - previous messages are prepended into the attacker-controlled request.
src/tools/deepseek-chat.ts:243 - attacker-provided user messages are appended into the reused session.
src/tools/deepseek-chat.ts:245 - assistant responses are appended back into the reused session.
src/tools/deepseek-sessions.ts:37 - deepseek_sessions list enumerates all active sessions.
src/tools/deepseek-sessions.ts:53 - each enumerated session ID is rendered back to the caller.

PoC Overview

Create a victim conversation with session_id = "victim-session".
Call deepseek_sessions with action = "list" and observe that victim-session is disclosed.
Call deepseek_chat again with session_id = "victim-session" from a separate attacker flow.
The upstream request now includes the victim's prior messages before the attacker's message.

Validation Environment

Local runtime verification on Windows host with Node.js v24.11.1, using the repository code at the tested commit and a local mock DeepSeek client to capture the effective message list passed upstream.

Impact

Any reachable caller can enumerate active session IDs and read prior conversation history stored in memory for other callers within the same server process. The same flaw also allows attacker-controlled continuation of another user's session state.

Remediation

Bind stored sessions to an authenticated transport session or other server-generated opaque identifier.
Do not allow arbitrary user-supplied session_id values to select existing server-side state.
Remove or restrict deepseek_sessions list so it does not disclose unrelated session IDs.
Reject reuse of a session unless the caller proves ownership of that session.

Attached Evidence

01_deepseek-mcp-server_cross_session_data_exposure.txt

Patches (maintainer)

Fixed in 1.7.0. The HTTP transport's SessionStore is no longer a process-wide singleton: each MCP HTTP session gets its own store, injected into the deepseek_chat and deepseek_sessions tool handlers, so a session_id from one HTTP session cannot read, enumerate, or clear another session's state. STDIO transport was never affected (one process per client). Integration tests in src/transport-isolation.test.ts assert the isolation.

Affected versions >=1.4.2, <1.7.0 are deprecated on npm. Upgrade to 1.7.0 or later.

Workaround

If upgrading is not immediately possible, run in STDIO transport (unset TRANSPORT=http) or stop the HTTP server.

Credit

Reported independently by @232-323 and @2REBCat (tested against 1.6.0). The same root cause was found and fixed concurrently by the maintainer during a security audit, shipped in 1.7.0. All parties are credited as finders.

Note on severity

A connected client could read other clients' conversation history (C:H), inject messages into their sessions (I:L), and clear or delete other clients' sessions (A:L). Scope is unchanged: the impact stays within the application's own authorization boundary, which is a cross-tenant authorization bypass, so S:U is correct.

Severity

8.6 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

Show details on source website

JSON

To clipboard

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        "name": "@arikusi/deepseek-mcp-server"
      },
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          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-55604"
  ],
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    "cwe_ids": [
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    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-25T18:37:27Z",
    "nvd_published_at": "2026-07-09T22:17:06Z",
    "severity": "HIGH"
  },
  "details": "# Cross-Session Data Exposure via Caller-Controlled `session_id`\n\nProject / Repository: `arikusi/deepseek-mcp-server`  \nAffected version / commit tested: `1.6.0` / `04f28be2c6e99d3d4e443a6ae37cc35f0a71554a`  \nVulnerability type: Authorization bypass / cross-session data exposure \nAuthentication required: No\n\n## Summary\nThe process-global `SessionStore` accepts caller-supplied `session_id` values without binding them to any authenticated principal or transport session. An attacker can enumerate active session IDs via `deepseek_sessions`, then reuse a victim-controlled `session_id` in `deepseek_chat` to retrieve and continue the victim\u0027s conversation context.\n\n## Affected Code\n- `src/session.ts:42` - caller-controlled session IDs are looked up directly from the global in-memory map.\n- `src/session.ts:67` - a new session is stored under the caller-controlled ID without ownership binding.\n- `src/session.ts:109` - `getMessages()` retrieves messages for any supplied session ID.\n- `src/tools/deepseek-chat.ts:195` - `deepseek_chat` creates or reuses the supplied `session_id`.\n- `src/tools/deepseek-chat.ts:197` - previous messages are loaded from the supplied `session_id`.\n- `src/tools/deepseek-chat.ts:198` - previous messages are prepended into the attacker-controlled request.\n- `src/tools/deepseek-chat.ts:243` - attacker-provided user messages are appended into the reused session.\n- `src/tools/deepseek-chat.ts:245` - assistant responses are appended back into the reused session.\n- `src/tools/deepseek-sessions.ts:37` - `deepseek_sessions list` enumerates all active sessions.\n- `src/tools/deepseek-sessions.ts:53` - each enumerated session ID is rendered back to the caller.\n\n## PoC Overview\n1. Create a victim conversation with `session_id = \"victim-session\"`.\n2. Call `deepseek_sessions` with `action = \"list\"` and observe that `victim-session` is disclosed.\n3. Call `deepseek_chat` again with `session_id = \"victim-session\"` from a separate attacker flow.\n4. The upstream request now includes the victim\u0027s prior messages before the attacker\u0027s message.\n\n## Validation Environment\nLocal runtime verification on Windows host with Node.js `v24.11.1`, using the repository code at the tested commit and a local mock DeepSeek client to capture the effective message list passed upstream.\n\n## Impact\nAny reachable caller can enumerate active session IDs and read prior conversation history stored in memory for other callers within the same server process. The same flaw also allows attacker-controlled continuation of another user\u0027s session state.\n\n## Remediation\n- Bind stored sessions to an authenticated transport session or other server-generated opaque identifier.\n- Do not allow arbitrary user-supplied `session_id` values to select existing server-side state.\n- Remove or restrict `deepseek_sessions list` so it does not disclose unrelated session IDs.\n- Reject reuse of a session unless the caller proves ownership of that session.\n\n## Attached Evidence\n[01_deepseek-mcp-server_cross_session_data_exposure.txt](https://github.com/user-attachments/files/26991248/01_deepseek-mcp-server_cross_session_data_exposure.txt)\n\n---\n\n## Patches (maintainer)\n\nFixed in **1.7.0**. The HTTP transport\u0027s `SessionStore` is no longer a process-wide singleton: each MCP HTTP session gets its own store, injected into the `deepseek_chat` and `deepseek_sessions` tool handlers, so a `session_id` from one HTTP session cannot read, enumerate, or clear another session\u0027s state. STDIO transport was never affected (one process per client). Integration tests in `src/transport-isolation.test.ts` assert the isolation.\n\nAffected versions `\u003e=1.4.2, \u003c1.7.0` are deprecated on npm. Upgrade to 1.7.0 or later.\n\n## Workaround\n\nIf upgrading is not immediately possible, run in STDIO transport (unset `TRANSPORT=http`) or stop the HTTP server.\n\n## Credit\n\nReported independently by @232-323 and @2REBCat (tested against 1.6.0). The same root cause was found and fixed concurrently by the maintainer during a security audit, shipped in 1.7.0. All parties are credited as finders.\n\n## Note on severity\n\nA connected client could read other clients\u0027 conversation history (C:H), inject messages into their sessions (I:L), and clear or delete other clients\u0027 sessions (A:L). Scope is unchanged: the impact stays within the application\u0027s own authorization boundary, which is a cross-tenant authorization bypass, so S:U is correct.",
  "id": "GHSA-fh3r-g96v-f578",
  "modified": "2026-08-25T18:37:27Z",
  "published": "2026-08-25T18:37:27Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/arikusi/deepseek-mcp-server/security/advisories/GHSA-fh3r-g96v-f578"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-55604"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/arikusi/deepseek-mcp-server"
    },
    {
      "type": "WEB",
      "url": "https://github.com/arikusi/deepseek-mcp-server/releases/tag/v1.7.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "@arikusi/deepseek-mcp-server has an Authorization Bypass Through User-Controlled Key"
}

Sightings

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Action not permitted

CVE-2026-55604 (GCVE-0-2026-55604)

FKIE_CVE-2026-55604

GHSA-FH3R-G96V-F578

Cross-Session Data Exposure via Caller-Controlled session_id

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Cross-Session Data Exposure via Caller-Controlled `session_id`