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

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

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.

Source published

9 Jul 2026 21:13:15 UTC

Source modified

10 Jul 2026 14:42:09 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

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.

Source published

Jul 9, 2026, 9:13:15 PM (timezone not stated)

Source modified

Jul 10, 2026, 2:42:09 PM (timezone not stated)

Observed here

7 Nov 2026 12:32:42 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

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.

Source published

9 Jul 2026 22:17:06 UTC

Source modified

25 Oct 2026 17:10:00 UTC

Observed here

27 Oct 2026 15:15:14 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

# 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 1. Create a victim conversation with `session_id = "victim-session"`. 2. Call `deepseek_sessions` with `action = "list"` and observe that `victim-session` is disclosed. 3. Call `deepseek_chat` again with `session_id = "victim-session"` from a separate attacker flow. 4. 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](https://github.com/user-attachments/files/26991248/01_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.

Source published

25 Aug 2026 18:37:27 UTC

Source modified

26 Aug 2026 01:18:34 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

Publisher rating · HIGH