GHSA-6cr4-ccf3-x7h4 CVE-2026-77259 PYSEC-2026-4086
MCP Atlassian: Arbitrary file read via confluence_upload_attachment allows exfiltration of server credentials
High
PyPI
- Severity
- 7.7 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 0.44%
- Chance of exploitation in the next 30 days. Higher than 38.41% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
- CWE-552 Files or Directories Accessible to External Parties
- Fix
0.22.0- Upgrade mcp-atlassian to this version or later
Description
Summary
Missing path validation in confluence_upload_attachment allows any authenticated MCP client to read arbitrary files from the server filesystem and exfiltrate their contents to Confluence. On Linux deployments, /proc/self/environ yields all runtime secrets in a single call.
Details
AttachmentsMixin.upload_attachment() in src/mcp_atlassian/confluence/attachments.py opens the caller-supplied file_path with no boundary check:
# line 477
files = {"file": (filename, open(file_path, "rb"))}
The download path was correctly hardened in GHSA-xjgw-4wvw-rgm4 via validate_safe_path() (lines 223, 272). That fix was not applied to the upload path, leaving it completely unguarded. The MCP tool layer (servers/confluence.py:1295) passes file_path verbatim with no additional sanitization.
PoC
# 1. Prepare target file (macOS demo; on Linux use /proc/self/environ directly)
cp ~/.aws/credentials /tmp/diagram.png
# 2. Call the MCP tool
confluence_upload_attachment(
content_id = "<any page attacker can edit>",
file_path = "/tmp/diagram.png"
)
# 3. Download attachment from Confluence — contains raw credentials
Tested on mcp-atlassian 0.21.1 against live Confluence Cloud. Attachment confirmed uploaded and retrieved with full credential content intact.
Impact
Any MCP client with edit access to one Confluence page can read arbitrary files from the server process. On shared/Docker deployments, /proc/self/environ exposes all users' API tokens in a single request. Exfiltrated Atlassian tokens provide persistent API access independent of MCP, surviving server shutdown or patching.
Incomplete fix of GHSA-xjgw-4wvw-rgm4 — arbitrary file read on upload mirrors the arbitrary file write on download fixed in that advisory.
Suggested Fix
# src/mcp_atlassian/confluence/attachments.py — upload_attachment()
# Add after abspath conversion, before open():
try:
validate_safe_path(file_path)
except ValueError as e:
return {"success": False, "error": str(e)}
Same fix required in upload_attachments() and src/mcp_atlassian/jira/attachments.py.
Affected versions
PyPI
| Package | Vulnerable | Fixed in |
|---|---|---|
| mcp-atlassian | < 0.22.0 |
0.22.0 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
mcp-atlassian PyPI → 0.22.0
- pip
pip install --upgrade "mcp-atlassian>=0.22.0"- poetry
poetry add "mcp-atlassian>=0.22.0"- uv
uv add "mcp-atlassian>=0.22.0"
Severity breakdown
CVSS 3.1 7.7
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- None
- Availability
- None
Weakness
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.
How to prevent it
- 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, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. When validating filenames, use stringent allowlists that limit the character set to be used. If feasible, only allow a single "." character in the filename to avoid weaknesses such as CWE-23, and exclude directory separators such as "/" to avoid CWE-36. Use a list of allowable file extensions, which will help to avoid CWE-434. Do not rely exclusively on a filtering mechanism that removes potentially dangerous characters. This is equivalent to a denylist, which may be incomplete (CWE-184). For example, filtering "/" is insufficient protection if the filesystem also supports the use of "\" as a directory separator. Another possible error could occur when the filtering is applied in a way that still produces dangerous data (CWE-182). For example, if "../" sequences are removed from the ".../...//" string in a sequential fashion, two instances of "../" would b
- 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.
- Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked. Use a built-in path canonicalization function (such as realpath() in C) that produces the canonical version of the pathname, which effectively removes ".." sequences and symbolic links (CWE-23, CWE-59). This includes: realpath() in C getCanonicalPath() in Java GetFullPath() in ASP.NET realpath() or abs_path() in Perl realpath() in PHP
- Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].
- Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
- Architecture and Design, Operation: Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.
- Architecture and Design: When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs. For example, ID 1 could map to "inbox.txt" and ID 2 could map to "profile.txt". Features such as the ESAPI AccessReferenceMap [REF-185] provide this capability.
- Architecture and Design, Operation: Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software. OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations. This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise. Be careful to avoid CWE-243 and other weaknesses related to jails.
- Architecture and Design, Operation: Store library, include, and utility files outside of the web document root, if possible. Otherwise, store them in a separate directory and use the web server's access control capabilities to prevent attackers from directly requesting them. One common practice is to define a fixed constant in each calling program, then check for the existence of the constant in the library/include file; if the constant does not exist, then the file was directly requested, and it can exit immediately. This significantly reduces the chance of an attacker being able to bypass any protection mechanisms that are in the base program but not in the include files. It will also reduce the attack surface.
- Implementation: Ensure that error messages only contain minimal details that are useful to the intended audience and no one else. The messages need to strike the balance between being too cryptic (which can confuse users) or being too detailed (which may reveal more than intended). The messages should not reveal the methods that were used to determine the error. Attackers can use detailed information to refine or optimize their original attack, thereby increasing their chances of success. If errors must be captured in some detail, record them in log messages, but consider what could occur if the log messages can be viewed by attackers. Highly sensitive information such as passwords should never be saved to log files. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a user account exists or not. In the context of path traversal, error messages which disclose path information can help attackers craft the appropriate attack strings to move through the file system hierarchy.
- Operation, Implementation: When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.
CWE-552: Files or Directories Accessible to External Parties
The product makes files or directories accessible to unauthorized actors, even though they should not be.
How to prevent it
- Implementation, System Configuration, Operation: When storing data in the cloud (e.g., S3 buckets, Azure blobs, Google Cloud Storage, etc.), use the provider's controls to disable public access.
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-g2r2-3j32-j27x MCP Atlassian: Reflected XSS in OAuth Setup Callback Handler | Medium | Also affects mcp-atlassian |
| GHSA-h7wj-5v37-59r2 MCP Atlassian: Path traversal in upload_attachment allows arbitrary file read (incomplete fix for CVE-2026-27825) | Medium | Also affects mcp-atlassian |
| GHSA-4596-2p6p-28cv MCP Atlassian: Insecure File Permissions on OAuth Token Storage | Medium | Also affects mcp-atlassian |
| GHSA-mfv2-4wvm-9pgp MCP Atlassian: Path traversal in upload_attachment allows arbitrary file read and exfiltration via MCP tool call | Medium | Also affects mcp-atlassian |
| GHSA-p6hp-93wp-fh6p MCP Atlassian: Path Traversal / Arbitrary File Read in confluence_upload_attachment MCP tool (incomplete fix of GHSA-xjgw-4wvw-rgm4) | High | Also affects mcp-atlassian |
| GHSA-mrq8-fv7v-hhjg MCP Atlassian: HTTP upload tools accept arbitrary server-local file paths | Medium | Also affects mcp-atlassian |
| GHSA-2xj6-xx86-cwwc MCP Atlassian: Arbitrary File Read & Exfiltration (Confused Deputy) in JIRA update_issue | High | Also affects mcp-atlassian |
| GHSA-vc25-24vv-fxxm MCP Atlassian: Jira and Confluence attachment upload tools can read arbitrary server-local files | High | Also affects mcp-atlassian |
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