Summary
MCP Atlassian: Arbitrary file read/exfiltration via uploadattachment missing validatesafe_path()
The upload_attachment method in confluence/attachments.py reads and uploads arbitrary local files to Confluence without calling validate_safe_path(). Both download methods (download_attachment at line 223, download_content_attachments at line 272) correctly call validate_safe_path() before writing files, but the upload path at lines 35-79 skips this check entirely.
An AI agent connected via MCP (or an attacker influencing that agent through prompt injection) can read any file on the host and exfiltrate it by uploading it as a Confluence page attachment.
Vulnerable Code
File: src/mcp_atlassian/confluence/attachments.py, lines 62-79
# No validate_safe_path() call anywhere in this method
if not os.path.isabs(file_path):
file_path = os.path.abspath(file_path)
if not os.path.exists(file_path):
return {"success": False, "error": f"File not found: {file_path}"}
filename = os.path.basename(file_path)
attachment = self._upload_attachment_direct(
content_id, file_path, filename, comment, minor_edit
)
The validate_safe_path function is already imported at line 9 of the same file, and used in the download methods. It was just not added to the upload path.
Proof of Concept
Tested with mcp-atlassian 0.21.1 on Python 3.11 (EC2, Amazon Linux 2023).
import inspect
from mcp_atlassian.confluence.attachments import AttachmentsMixin
# Confirm: no validate_safe_path in upload
source = inspect.getsource(AttachmentsMixin.upload_attachment)
assert "validate_safe_path" not in source # passes
# Confirm: validate_safe_path IS in downloads
assert "validate_safe_path" in inspect.getsource(AttachmentsMixin.download_attachment) # passes
assert "validate_safe_path" in inspect.getsource(AttachmentsMixin.download_content_attachments) # passes
An MCP tool call like this reads /etc/passwd and uploads it to Confluence:
{"tool": "confluence_upload_attachment", "arguments": {"content_id": "123456", "file_path": "/etc/passwd"}}
Impact
Exfiltration of any file readable by the MCP server process: SSH keys, AWS credentials, .env files, /etc/passwd, application secrets. Data leaves the local machine and lands on a remote Confluence instance accessible to other users.
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
CVE-2026-77258 has a CVSS score of 7.7 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.22.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Add validate_safe_path(file_path) before the os.path.exists() check in upload_attachment, matching the existing pattern in the download methods. The function is already imported.
Frequently Asked Questions
- What is CVE-2026-77258? CVE-2026-77258 is a high-severity path traversal vulnerability in mcp-atlassian (pip), affecting versions < 0.22.0. It is fixed in 0.22.0. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- How severe is CVE-2026-77258? CVE-2026-77258 has a CVSS score of 7.7 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of mcp-atlassian are affected by CVE-2026-77258? mcp-atlassian (pip) versions < 0.22.0 is affected.
- Is there a fix for CVE-2026-77258? Yes. CVE-2026-77258 is fixed in 0.22.0. Upgrade to this version or later.
- Is CVE-2026-77258 exploitable, and should I be worried? Whether CVE-2026-77258 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-77258 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-77258? Upgrade
mcp-atlassianto 0.22.0 or later.