CVE-2026-77257: MCP Atlassian: HTTP upload tools accept arbitrary server-local file paths

The project treats HTTP deployment as a first-class mode, and the HTTP host defaults to 0.0.0.0. In that mode the code treats "the MCP process can read this file" as "the caller may upload it". That holds for single-user stdio, not for shared servers.

The Confluence upload tool exposes a file_path. In confluence/attachments.py the path is made absolute, checked for existence and opened for a multipart upload. Jira's update_issue takes attachments as a JSON array or comma-separated list, and jira/attachments.py repeats the pattern. The project already has validate_safe_path and applies it to download destinations, but not to upload sources.

An authenticated caller, or a prompt-injected agent with tool access, needs a write tool and an issue or page they can write to. They then read the attached file in Atlassian. In Docker or Kubernetes setups that mount .env or token files, that exposes API tokens, OAuth credentials and service configuration. The reporter says it is not remote code execution. Severity is medium for single-user stdio or tightly scoped tokens, and high for shared HTTP servers.

mcp-atlassian below 0.22.0, mainly deployments using the sse or streamable-http transport with write tools enabled. All toolsets are enabled when TOOLSETS is unset, and READ_ONLY_MODE is off by default.

pip show mcp-atlassian

On Docker, check the image tag in your compose file.

Upgrade to 0.22.0:

pip install --upgrade mcp-atlassian==0.22.0

The fix landed in pull request 1448. For interim hardening, the docs describe READ_ONLY_MODE=true, which blocks the write tools that perform uploads. Bind the HTTP service to a trusted interface instead of the default 0.0.0.0, and keep secrets out of files the container can read.

Look for attachments in Jira or Confluence added by the integration account whose filenames match secrets, such as .env, token or credentials files. In the server's request logs, check for jira_update_issue calls with an attachments value or Confluence upload calls with file_path set to an absolute path or containing .., especially from unfamiliar callers. If an agent drives the server, Beam's record of its MCP tool calls can show which session sent them.

sooperset/mcp-atlassian: HTTP upload tools can attach arbitrary server-local files

Date: 2026-05-05 Target: sooperset/mcp-atlassian Commit: d8bc78698a63cb6b321c7ca796d6329d448f7f6d

Summary

mcp-atlassian supports HTTP/SSE deployment for persistent, remote, and multi-user use. In that mode, write-capable Jira and Confluence attachment flows accept caller-controlled server-local file paths and read those paths without an upload-source allowlist or base directory restriction.

An authenticated caller, or a prompt-injected agent with tool-call capability, can cause the MCP server process to read a local file it can access and attach that file into a Jira issue or Confluence page using configured Atlassian credentials.

This is distinct from the prior download-path advisory: that issue was an arbitrary file write sink. This path is upload-source local file disclosure.

Impact

Impact is local file disclosure through an authenticated Atlassian attachment write. In Docker/Kubernetes deployments that mount .env or token material into the service, exposed files may include API tokens, OAuth credentials, service configuration, or other local secrets readable by the MCP process.

The issue is bounded by tool access and Atlassian permissions: the attacker needs an MCP call path to a write tool and an issue/page where the attachment can be written. It is not direct RCE.

Severity is Medium-to-High depending on deployment:

• Medium for single-user/local stdio usage or tightly scoped tokens.
• High where HTTP/streamable deployments are shared, write tools are exposed, and the server has access to secrets or broad filesystem mounts.

Source Evidence

HTTP/multi-user deployment is first-class:

• docs/http-transport.mdx:1-7 describes running as a persistent HTTP service for multi-user and remote deployment.
• docs/http-transport.mdx:10-13 lists SSE and streamable-http endpoints.
• docs/http-transport.mdx:88-90 says both HTTP transports support per-request authentication.
• docs/advanced/docker-production.mdx:25-37 shows Docker deployment with .env, exposed ports, and HOST=0.0.0.0.
• docs/advanced/docker-production.mdx:91-103 shows Atlassian credentials stored in .env.
• src/mcp_atlassian/__init__.py:359-363 defaults HTTP host to 0.0.0.0 unless overridden.

The Confluence upload path reads caller-chosen server-local files:

• src/mcp_atlassian/servers/confluence.py:1290-1315 exposes file_path and explicitly accepts absolute or relative paths.
• src/mcp_atlassian/servers/confluence.py:1356-1363 passes file_path to confluence_fetcher.upload_attachment.
• src/mcp_atlassian/confluence/attachments.py:62-70 only converts relative paths to absolute and checks existence.
• src/mcp_atlassian/confluence/attachments.py:77-80 passes the path to _upload_attachment_direct.
• src/mcp_atlassian/confluence/attachments.py:477 opens file_path for the multipart upload.

The Jira update path can also upload caller-chosen server-local files:

• src/mcp_atlassian/servers/jira.py:1564-1568 exposes jira_update_issue as a write tool in toolset:jira_issues.
• src/mcp_atlassian/servers/jira.py:1609-1618 accepts attachments as a JSON array or comma-separated list of file paths.
• src/mcp_atlassian/servers/jira.py:1648-1674 parses those file paths and adds them to the update payload.
• src/mcp_atlassian/jira/issues.py:1132-1137 forwards attachments to upload_attachments.
• src/mcp_atlassian/jira/attachments.py:372-389 converts relative paths to absolute, checks existence, opens the path, and passes it to jira.add_attachment.

Existing controls do not authorize the upload source path:

• src/mcp_atlassian/utils/decorators.py:45-72 blocks writes only when read-only mode is enabled.
• src/mcp_atlassian/servers/main.py:276-279 filters write tools out of listing only in read-only mode.
• src/mcp_atlassian/utils/toolsets.py:158-183 currently enables all toolsets when TOOLSETS is unset.
• docs/advanced/docker-production.mdx:109-119 documents READ_ONLY_MODE=true as an optional production hardening setting, not a default.
• src/mcp_atlassian/confluence/attachments.py:217-223 and src/mcp_atlassian/jira/attachments.py:37-43 show validate_safe_path exists for download destinations, but no equivalent upload-source containment is applied.

Root cause

The codebase already has a path-containment primitive (validate_safe_path) and applies it to download destinations to prevent writes outside a configured base directory — that is, it correctly defends the filesystem-write side of the boundary. But the upload-source side of the same boundary is not defended at all: the Confluence and Jira attachment paths convert caller-supplied paths to absolute, check that the file exists, open it, and stream the bytes to Atlassian, with no equivalent "must resolve inside an upload base directory" check. The authorization model implicitly treats "the MCP process can read this file" as equivalent to "the MCP caller is authorized to upload this file," which is correct only for single-user stdio mode. For HTTP/SSE multi-user mode (which the project documents as first-class and ships with HOST=0.0.0.0), it is not — caller identity and process filesystem-read capability are different boundaries. The structural fix is to apply the existing validate_safe_path containment primitive to upload-source paths under a separate UPLOAD_BASE_DIR configuration, and to disable server-local upload tools by default in HTTP transport mode unless that base directory is configured.

Auth boundary violated

Boundary: Per-user resource ownership (in HTTP/SSE multi-user mode, an authenticated MCP caller's tool surface should expose only files the caller is authorized to upload — not arbitrary files in the MCP process's filesystem view, including operator-mounted secrets and other tenants' data).

Respected at: src/mcp_atlassian/confluence/attachments.py:217-223 and src/mcp_atlassian/jira/attachments.py:37-43 (validate_safe_path is correctly applied to download-destination paths to prevent writes outside a base directory).

Violated at: src/mcp_atlassian/confluence/attachments.py:62-70,77-80,477 (Confluence upload path: relative-to-absolute conversion, existence check, then open(file_path), with no validate_safe_path call against an upload base directory) and src/mcp_atlassian/jira/attachments.py:372-389 (Jira upload path: identical pattern). The boundary is silently dropped: the same containment primitive that defends the download side is not invoked on the upload side.

Reproduction

Observed:

CONFLUENCE_SINK content_id=attacker-visible-page-id filename=mcp-atlassian-poc-secret.txt
CONFLUENCE_EXFIL_MARKER=FAKE_SECRET_MARKER_DO_NOT_PUBLISH_REAL_SECRET
CONFLUENCE_RESULT={'success': True, 'filename': 'mcp-atlassian-poc-secret.txt'}
JIRA_SINK issue_key=ATTACKER-1 filename=mcp-atlassian-poc-secret.txt
JIRA_EXFIL_MARKER=FAKE_SECRET_MARKER_DO_NOT_PUBLISH_REAL_SECRET
JIRA_RESULT={'success': True, 'filename': 'mcp-atlassian-poc-secret.txt'}

The PoC uses fake upload sinks and does not contact Atlassian. It demonstrates the vulnerable behavior: a caller-provided absolute server-local path is accepted, read, and delivered to the attachment sink.

Known Issue / Dupe Checks

Known advisories are different:

• GHSA-xjgw-4wvw-rgm4: arbitrary file write through unconstrained Confluence download path.
• GHSA-7r34-79r5-rcc9: SSRF through unvalidated Atlassian URL headers.

Closest public non-security overlap:

• issue #618: usability report that upload requires server-side paths.
• issue #1163: unrelated upload failure on Data Center.
• PRs #987 / #949: download-path hardening, not upload-source path containment.

No public issue/PR/advisory found for upload-side arbitrary local file read.

Suggested Fix

Add an explicit upload source policy, for example:

• require MCP_ATLASSIAN_UPLOAD_BASE_DIR for server-local upload tools in HTTP/SSE/streamable mode
• reject absolute paths unless they resolve inside that configured base directory
• apply validate_safe_path(path, base_dir=upload_base_dir) before existence checks or reads
• consider disabling server-local upload tools by default in HTTP mode unless an upload directory is configured

Add regression tests for both Confluence and Jira upload paths:

• reject /etc/passwd
• reject ../../../etc/passwd
• reject symlinks escaping the upload base
• accept a file inside the configured upload directory
• verify READ_ONLY_MODE=true still blocks the write independently