4.6

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2026-32947

CVE-2026-32947: Egress Policy Bypass via DNS over HTTPS (DoH) in Harden-Runner (Community Tier)

Harden-Runner is a CI/CD security agent that works like an EDR for GitHub Actions runners. In versions 2.15.1 and below, a DNS over HTTPS (DoH) vulnerability allows attackers to bypass egress-policy: block network restrictions by tunneling exfiltrated data through permitted HTTPS endpoints like dns.google. The attack works by encoding sensitive data (e.g., the runner's hostname) as subdomains in DoH queries, which appear as legitimate HTTPS traffic to Harden-Runner's domain-based filtering but are ultimately forwarded to an attacker-controlled domain. This effectively enables data exfiltration without directly connecting to any blocked destination. Exploitation requires the attacker to already have code execution within the GitHub Actions workflow. The issue was fixed in version 2.16.0.

(GitHub Advisory)

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CVE-2026-32947

CVE-2026-32947:

4.6

CVSS Score

4.0

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
step-security/harden-runner	actions	<= 2.15.1	2.16.0

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability GHSA-46g3-37rh-v698 in step-security/harden-runner allows for egress policy bypass via DNS over HTTPS. The investigation started by analyzing the provided patch information for harden-runner. The fix in harden-runner was to upgrade the version of its dependency, step-security/agent, from v0.14.3 to v0.14.4. This indicates the root cause of the vulnerability lies within the step-security/agent repository.

By comparing the commits between v0.14.3 and v0.14.4 of step-security/agent, the key change was identified in the firewall.go file, specifically within the addBlockRules function. Before the patch, this function created a broad iptables rule that allowed any process to make outbound connections to the specified DNS servers. This created a loophole where an attacker with code execution within the GitHub Actions workflow could use DNS-over-HTTPS to exfiltrate data, bypassing the intended network restrictions.

The patch mitigates this by adding a UID-based owner check (--uid-owner) to the iptables rule. This ensures that only the agent process itself is permitted to communicate with the DNS servers for legitimate DNS resolution, effectively closing the exfiltration channel for other processes running in the workflow. Therefore, the main.addBlockRules function in step-security/agent is the identified vulnerable function.

Vulnerable functions

main.addBlockRules

firewall.go

The function `addBlockRules` in `firewall.go` in the `step-security/agent` dependency was responsible for setting up `iptables` rules to control network egress. The vulnerability existed because the function added a rule that allowed any process to send TCP traffic to configured DNS servers. An attacker with code execution in the workflow could exploit this to bypass network restrictions by using DNS-over-HTTPS (DoH) to exfiltrate data. The fix restricts this traffic to only the agent process itself by adding a `--uid-owner` check to the `iptables` rule, ensuring only the agent can communicate with the DNS servers.

Vulnerability Intelligence
Miggo AI

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WAF Rule

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Reasoning

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