CVE-2026-77265: mcp-atlassian SSRF Vulnerability via DNS Rebinding in Header-Based Authentication Flow
Summary
CVE-2026-77265: MCP Atlassian: SSRF via DNS Rebinding in Header-Based Authentication Flow. Affects mcp-atlassian versions < 0.22.0. Fixed in 0.22.0. How to fix ↓
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Background
mcp-atlassian is a Python package that integrates with Atlassian products, allowing users to automate tasks and manage resources effectively. It supports header-based authentication, which is a common method for securing API access. However, this package has a vulnerability that exposes it to Server-Side Request Forgery (SSRF) attacks due to improper DNS resolution handling.
Vulnerability Detail
The vulnerability arises from the SSRF protection mechanism in the header-based authentication flow, which employs a validate-then-use pattern susceptible to DNS rebinding attacks. The function validate_url_for_ssrf checks the hostname's DNS resolution and ensures it is globally routable. However, the actual HTTP request is made later, allowing an attacker to change the DNS record to point to an internal IP address. This flaw can lead to unauthorized access to internal services and cloud metadata, potentially exposing sensitive information such as IAM credentials.
How To Fix
Latest published version: 0.23.1 as of 23 Oct 2026
pip install --upgrade "mcp-atlassian==0.23.1"Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
0.22.0
This is the first release that contains the fix.
pip install --upgrade "mcp-atlassian==0.22.0"Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, you can implement additional network security measures to restrict access to internal IP addresses and monitor DNS resolutions closely. However, the best approach is to update to the patched version of the package.
Conclusion
The mcp-atlassian package is vulnerable to SSRF attacks due to improper DNS resolution handling in its header-based authentication flow. It is crucial to update to the patched version (0.22.0 or later) to mitigate this risk. Additionally, users should monitor their applications for potential exposure to this vulnerability.
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FAQ
CVE-2026-77265 is a vulnerability in the mcp-atlassian package that allows for SSRF attacks via DNS rebinding in the header-based authentication flow.
In a DNS rebinding attack, an attacker can manipulate DNS records to redirect requests from a public IP to an internal IP, potentially exposing sensitive services.
The vulnerability can lead to unauthorized access to cloud metadata, internal network scanning, and exposure of sensitive information such as IAM credentials.
You can use the Vulert playground at Vulert Scanner to check if your application is affected by this vulnerability without requiring signup.
The CVSS score of this vulnerability is 5.9, indicating a moderate severity level.
References
Related vulnerabilities
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