CVE-2026-77248: MCP Atlassian — HIGH

Q: Is CVE-2026-77248 actively exploited?

No confirmed active exploitation of CVE-2026-77248 has been reported, but organizations should still patch proactively.

Q: How to fix CVE-2026-77248?

Update to patched version: MCP Atlassian 0.22.0.

Q: What is the CVSS score for CVE-2026-77248?

CVE-2026-77248 has a CVSS v3.1 base score of 8.6 (HIGH).

### Summary In the documented multi-user HTTP deployment (`--transport streamable-http` with global operator Atlassian credentials), sooperset/mcp-atlassian exposes all tools to **unauthenticated network clients**, and the `upload_attachment` tool reads an attacker-supplied `file_path` with **no...

Full CISO analysis pending enrichment.

What systems are affected?

Package	Ecosystem	Vulnerable Range	Patched
MCP Atlassian	pip	< 0.22.0	`0.22.0`
1 dependents 85% patched ~3d to patch Full package profile →

Do you use MCP Atlassian? You're affected.

How severe is it?

CVSS 3.1

8.6 / 10

EPSS

N/A

Exploitation Status

No known exploitation

Sophistication

N/A

What is the attack surface?

AV Network

AC Low

PR None

UI None

S Changed

C High

I None

A None

What should I do?

Patch available

Update MCP Atlassian to version 0.22.0

Which compliance frameworks are affected?

Compliance analysis pending. Sign in for full compliance mapping when available.

Frequently Asked Questions

What is CVE-2026-77248?

### Summary In the documented multi-user HTTP deployment (`--transport streamable-http` with global operator Atlassian credentials), sooperset/mcp-atlassian exposes all tools to **unauthenticated network clients**, and the `upload_attachment` tool reads an attacker-supplied `file_path` with **no path validation**. Chained, an unauthenticated network attacker reads arbitrary files on the MCP server host (e.g. `/proc/self/environ` → the operator's Atlassian API token + `.env` secrets, `~/.ssh/id_rsa`, `/etc/passwd`) by uploading them to an attacker-chosen page/issue and reading them back. ### Details **Missing authentication (transport):** - streamable-http binds `0.0.0.0` by default (`src/mcp_atlassian/__init__.py:151`). - The OAuth-proxy auth provider is opt-in (`ATLASSIAN_OAUTH_PROXY_ENABLE`, default false), so `main_mcp` is built with `auth=None` (`src/mcp_atlassian/servers/main.py:724-731, 813-817`). - `UserTokenMiddleware._parse_auth_header` sets `auth_validation_error` only for a *malformed* Authorization header; a request with **no** Authorization header passes through (`main.py:416-446, 582-595`). - `_get_fetcher` then falls through to the global credential fallback using the operator's `.env` Atlassian token (`src/mcp_atlassian/servers/dependencies.py:644-676`). `check_write_access` gates only on read-only mode, not auth → read **and** write tools reachable. **Arbitrary file read (sink):** - `upload_attachment`'s `file_path` flows unsanitized into `open(file_path, 'rb')` — Confluence `src/mcp_atlassian/confluence/attachments.py:477` (from `servers/confluence.py:1294-1369`); Jira `src/mcp_atlassian/jira/attachments.py:386` (from `servers/jira.py:1609-1673`). No `validate_safe_path` / allowlist (contrast the download flow, hardened after CVE-2026-27825). ### Proof of Concept ``` # unauthenticated (no Authorization header) against a default streamable-http deployment: tools/call upload_attachment { "file_path": "/proc/self/environ", "page_id": "<attacker-chosen>" } # then read it back: tools/call download_attachment { ... } # returns the bytes (base64) -> operator's ATLASSIAN token + .env secrets ``` ### Impact Unauthenticated arbitrary local file read on the MCP server host — including the operator's Atlassian API token and `.env` secrets — a boundary the Atlassian-scoped tool must not cross, plus unauthenticated use of every read/write Atlassian tool as the operator's (often admin) principal. Distinct from GHSA-xjgw-4wvw-rgm4 (file *write* via download_path) and GHSA-7r34-79r5-rcc9 (URL-header SSRF). ### Suggested fix Require authentication on the streamable-http transport by default (do not fall back to operator global credentials for unauthenticated requests); apply `validate_safe_path`/allowlist to `file_path` in `upload_attachment` as the download flow already does. ### Affected `mcp-atlassian` <= 0.21.1.

Is CVE-2026-77248 actively exploited?

No confirmed active exploitation of CVE-2026-77248 has been reported, but organizations should still patch proactively.

How to fix CVE-2026-77248?

Update to patched version: MCP Atlassian 0.22.0.

What is the CVSS score for CVE-2026-77248?

CVE-2026-77248 has a CVSS v3.1 base score of 8.6 (HIGH).

What are the technical details?

Original Advisory

### Summary In the documented multi-user HTTP deployment (`--transport streamable-http` with global operator Atlassian credentials), sooperset/mcp-atlassian exposes all tools to **unauthenticated network clients**, and the `upload_attachment` tool reads an attacker-supplied `file_path` with **no path validation**. Chained, an unauthenticated network attacker reads arbitrary files on the MCP server host (e.g. `/proc/self/environ` → the operator's Atlassian API token + `.env` secrets, `~/.ssh/id_rsa`, `/etc/passwd`) by uploading them to an attacker-chosen page/issue and reading them back. ### Details **Missing authentication (transport):** - streamable-http binds `0.0.0.0` by default (`src/mcp_atlassian/__init__.py:151`). - The OAuth-proxy auth provider is opt-in (`ATLASSIAN_OAUTH_PROXY_ENABLE`, default false), so `main_mcp` is built with `auth=None` (`src/mcp_atlassian/servers/main.py:724-731, 813-817`). - `UserTokenMiddleware._parse_auth_header` sets `auth_validation_error` only for a *malformed* Authorization header; a request with **no** Authorization header passes through (`main.py:416-446, 582-595`). - `_get_fetcher` then falls through to the global credential fallback using the operator's `.env` Atlassian token (`src/mcp_atlassian/servers/dependencies.py:644-676`). `check_write_access` gates only on read-only mode, not auth → read **and** write tools reachable. **Arbitrary file read (sink):** - `upload_attachment`'s `file_path` flows unsanitized into `open(file_path, 'rb')` — Confluence `src/mcp_atlassian/confluence/attachments.py:477` (from `servers/confluence.py:1294-1369`); Jira `src/mcp_atlassian/jira/attachments.py:386` (from `servers/jira.py:1609-1673`). No `validate_safe_path` / allowlist (contrast the download flow, hardened after CVE-2026-27825). ### Proof of Concept ``` # unauthenticated (no Authorization header) against a default streamable-http deployment: tools/call upload_attachment { "file_path": "/proc/self/environ", "page_id": "<attacker-chosen>" } # then read it back: tools/call download_attachment { ... } # returns the bytes (base64) -> operator's ATLASSIAN token + .env secrets ``` ### Impact Unauthenticated arbitrary local file read on the MCP server host — including the operator's Atlassian API token and `.env` secrets — a boundary the Atlassian-scoped tool must not cross, plus unauthenticated use of every read/write Atlassian tool as the operator's (often admin) principal. Distinct from GHSA-xjgw-4wvw-rgm4 (file *write* via download_path) and GHSA-7r34-79r5-rcc9 (URL-header SSRF). ### Suggested fix Require authentication on the streamable-http transport by default (do not fall back to operator global credentials for unauthenticated requests); apply `validate_safe_path`/allowlist to `file_path` in `upload_attachment` as the download flow already does. ### Affected `mcp-atlassian` <= 0.21.1.

Weaknesses (CWE)

CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') Primary CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') CWE-306 Missing Authentication for Critical Function

CWE-22 — Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'): The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

[Implementation] Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylis
[Architecture and Design] For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

Source: MITRE CWE corpus.