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High, CVSS 7.7amended

MCP Atlassian: Arbitrary file read/exfiltration via upload_attachment missing validate_safe_path()

CVE-2026-77258GHSA-93xw-j965-9mx3

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (mcp-atlassian 0.22.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.7 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N
EPSS
  • CVE-2026-77258: 0.37% estimated exploitation activity in the next 30 days; percentile 31.47 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary The uploadattachment method in confluence/attachments.py reads and uploads arbitrary local files to Confluence without calling validatesafepath(). Both download methods (downloadattachment at line 223, downloadcontentattachments at line 272) correctly call validatesafepath() 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/mcpatlassian/confluence/attachments.py, lines 62-79 The validatesafepath 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). An MCP tool call like this reads /etc/passwd and uploads it to Confluence: Impact Exfiltration of any file readable…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-93xw-j965-9mx3

  2. Revision 2 · amended ·

    Amended from osv record GHSA-93xw-j965-9mx3

  3. Revision 1 · created ·

    Published from ghsa record GHSA-93xw-j965-9mx3

Agent brief

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# Patch Next advisory brief: CVE-2026-77258

Advisory: MCP Atlassian: Arbitrary file read/exfiltration via upload_attachment missing validate_safe_path()
IDs: CVE-2026-77258, GHSA-93xw-j965-9mx3
Record: https://patchnext.com/advisories/cve-2026-77258 (revision 3, source checked 26 Oct 2026, 13:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: mcp-atlassian 0.22.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI mcp-atlassian: affected < 0.22.0; fixed in 0.22.0

## Suggested inspection (read-only)
- `python -m pip show mcp-atlassian`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on mcp-atlassian.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-93xw-j965-9mx3 (GitHub-reviewed advisory GHSA-93xw-j965-9mx3 lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0)
- Verified: https://osv.dev/vulnerability/GHSA-93xw-j965-9mx3 (OSV record GHSA-93xw-j965-9mx3 lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0 (fixed))

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