CVE-2026-32947
DNS over HTTPS Bypass in Harden-Runner Enables Data Exfiltration
Publication date: 2026-03-20
Last updated on: 2026-03-24
Assigner: GitHub, Inc.
Description
Description
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| stepsecurity | harden-runner | to 2.16.0 (exc) |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-693 | The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product. |
| CWE-863 | The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
[{'type': 'paragraph', 'content': 'CVE-2026-32947 is a vulnerability in Harden-Runner, a security agent for GitHub Actions runners that enforces network egress policies. In versions 2.15.1 and below of the Community Tier, attackers who already have code execution within a GitHub Actions workflow can bypass network restrictions by exploiting DNS over HTTPS (DoH).'}, {'type': 'paragraph', 'content': "The attack works by encoding sensitive data, such as the runner's hostname, into DNS queries sent over HTTPS to allowed endpoints like Google's DoH resolver (dns.google). These queries appear as legitimate HTTPS traffic and bypass Harden-Runner's domain-based filtering, allowing data to be exfiltrated to attacker-controlled domains without directly connecting to blocked destinations."}, {'type': 'paragraph', 'content': 'This vulnerability affects only the Community Tier of Harden-Runner and was fixed in version 2.16.0.'}] [1]
How can this vulnerability impact me? :
[{'type': 'paragraph', 'content': "If exploited, this vulnerability allows an attacker with existing code execution in a GitHub Actions workflow to bypass Harden-Runner's network egress restrictions and exfiltrate sensitive data covertly."}, {'type': 'paragraph', 'content': "This means that even if outbound network connections are restricted to certain domains and ports, an attacker can tunnel data through permitted HTTPS endpoints using DNS over HTTPS queries, effectively leaking information such as the runner's hostname or other sensitive data."}, {'type': 'paragraph', 'content': 'The impact is limited to environments using the Community Tier of Harden-Runner versions 2.15.1 and below, and only if the attacker already has code execution within the workflow.'}] [1]
How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:
I don't know
How can this vulnerability be detected on my network or system? Can you suggest some commands?
Detection of this vulnerability involves monitoring for unusual DNS over HTTPS (DoH) traffic that encodes sensitive data as subdomains in DNS queries sent through permitted HTTPS endpoints like dns.google.
Since the attack tunnels exfiltrated data via DoH queries appearing as legitimate HTTPS traffic, network monitoring tools should be configured to inspect DoH traffic patterns and query contents for suspicious subdomain encodings.
Commands to detect such activity could include capturing and analyzing HTTPS traffic to known DoH resolvers (e.g., 8.8.8.8) and inspecting DNS query subdomains for encoded data.
- Use packet capture tools like tcpdump or Wireshark to filter HTTPS traffic to DoH endpoints: tcpdump -i <interface> host 8.8.8.8 and port 443
- Analyze captured traffic for DNS queries embedded in HTTPS requests that contain unusual or encoded subdomain patterns.
- Review GitHub Actions workflow logs for unexpected network connections or commands that might execute code capable of exploiting this vulnerability.
What immediate steps should I take to mitigate this vulnerability?
The primary mitigation step is to upgrade Harden-Runner to version 2.16.0 or later, where this DNS over HTTPS (DoH) exfiltration vulnerability has been fixed.
For users of the Community Tier of Harden-Runner, applying this update will enforce proper egress policy blocking and prevent attackers from bypassing network restrictions via DoH.
Enterprise Tier users are not impacted by this vulnerability and do not require any action.
Additionally, review and restrict code execution permissions within GitHub Actions workflows to minimize the risk of attackers gaining the initial code execution required to exploit this vulnerability.