# CVE-2026-77265: Atlassian MCP Server SSRF via DNS rebinding in header authentication

Source: https://junglewise.ai/threats/cve-2026-77265-atlassian-mcp-server-ssrf-via-dns-rebinding-in-header  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-22. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-77265 · Severity: medium · CVSS 5.9 · Published 2026-09-22

The Atlassian Model Context Protocol (MCP) server validates URLs in HTTP headers for security before making requests, but an attacker can exploit DNS rebinding to bypass this check. By rapidly changing DNS records between validation and actual request execution, an attacker can redirect requests to internal cloud metadata services or internal network resources, potentially stealing credentials and accessing sensitive data.

Technologies: [mcp-atlassian (PyPI)](https://junglewise.ai/threats/technologies/mcp-atlassian). Vendors: [Atlassian](https://junglewise.ai/threats/vendors/atlassian), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-77265 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-77265 being exploited in the wild.

**How severe is CVE-2026-77265?** Medium severity, with a CVSS score of 5.9, published 22 September 2026.

**Which products and versions are affected?** mcp-atlassian (PyPI) < 0.22.0, ECOSYSTEM:introduced=0,fixed=0.22.0.

**Is there a fix for CVE-2026-77265?** Yes. mcp-atlassian (PyPI): upgrade to 0.22.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-77265 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-77265?** Check whether you run Atlassian MCP Atlassian Server or mcp-atlassian (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- mcp-atlassian (PyPI): upgrade to 0.22.0 or later

  ```sh
  pip install "mcp-atlassian>=0.22.0"
  ```


## Technical details

This is a classic time-of-check-time-of-use (TOCTOU) vulnerability in the SSRF protection mechanism. The validate_url_for_ssrf function in urls.py performs a DNS lookup and verifies the resolved IP is globally routable; however, the HTTP request using the requests library happens later in dependencies.py with a separate DNS resolution. An attacker can register a domain with a short TTL that initially resolves to a legitimate public IP (passing validation), then immediately changes the DNS record to resolve to an internal IP like 169.254.169.254 (AWS metadata service) before the HTTP request is made. The SSRF redirect hook only validates redirect Location headers, not the initial connection target, leaving the initial DNS resolution unprotected. The vulnerability requires multiple attempts (probabilistic exploitation) and currently only affects deployments using the header_pat authentication branch.

## Affected products

- Atlassian MCP Atlassian Server

## Identifiers

- CVE-2026-77265
- GHSA-49xv-9743-pw8w
- PYSEC-2026-4083

## Timeline

- 2026-09-22: disclosed

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- [sooperset mcp-atlassian path traversal in confluence_upload_attachment](https://junglewise.ai/threats/cve-2026-77262-sooperset-mcp-atlassian-path-traversal-in-confluence-upload)