CVE-2026-27825: MCP Atlassian has an arbitrary file write leading to arbitrary code execution via unconstrained download_path in confluence_download_attachment

Should you act?

Critical, preconditions apply

Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 1.5%, percentile 74: FIRST’s model estimates a 1.5% chance of exploitation activity in the next 30 days, higher than 74% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Needs an account (low (any account)). Exposure depends on who can log in.
• Only applies if your dependency tree includes mcp-atlassian (PyPI) < 0.17.0, fixed in 0.17.0. Check your lockfile, including transitive dependencies.

What it is

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to version 0.17.0, the confluencedownloadattachment MCP tool accepts a downloadpath parameter that is written to without any directory boundary enforcement. An attacker who can call this tool and supply or access a Confluence attachment with malicious content can write arbitrary content to any path the server process has write access to. Because the attacker controls both the write destination and the written content (via an uploaded Confluence attachment), this constitutes for arbitrary code execution (for example, writing a valid cron entry to /etc/cron.d/ achieves code execution within one scheduler cycle with no server restart required). Version 0.17.0 fixes the issue.

From the GitHub advisory

Summary The confluencedownloadattachment MCP tool accepts a downloadpath parameter that is written to without any directory boundary enforcement. An attacker who can call this tool and supply or access a Confluence attachment with malicious content can write arbitrary content to any path the server process has write access to. Because the attacker controls both the write destination and the written content (via an uploaded Confluence attachment), this constitutes for arbitrary code execution (for example, writing a valid cron entry to /etc/cron.d/ achieves code execution within one scheduler cycle with no server restart required).

Details The tool parameter is defined in src/mcpatlassian/servers/confluence.py:~1275 without any path restriction:

python downloadpath: Annotated[ str, Field( description=( "Full path where the file should be saved. Can be absolute or relative. " "Examples: './downloads/report.pdf', '/tmp/image.png', 'C:\\\\temp\\\\file.docx'. " "Parent directory will be created if it doesn't exist." ) ), ],

The implementation at src/mcpatlassian/confluence/attachments.py:183–200:

if not os.path.isabs(targetpath): targetpath = os.path.abspath(targetpath) # normalizes path, no restriction

Weakness type: CWE-22, CWE-73.

Product: mcp-atlassian (PyPI) · Assigned by: GitHub_M · Published: 2026-03-10

Affected and fixed versions

Severity scores

• Attack vector: adjacent network only
• Attack complexity: low
• Privileges required: low (any account)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 1.53% probability of exploitation activity in the next 30 days; percentile 74.

Timeline

• 2026-03-10 — CVE record last updated
• 2026-03-10 — CVE record published by GitHub_M
• 2026-03-10 — GitHub-reviewed advisory GHSA-xjgw-4wvw-rgm4 published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-xjgw-4wvw-rgm4 github.com
2. CVE.org record CVE-2026-27825 cve.org
3. NVD entry CVE-2026-27825 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

Critical PyPI advisories · Today’s Security Digest