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CVE-2026-18428 is a denial-of-service vulnerability affecting GitHub Enterprise Server instances that process repository release notes configuration files. When a repository maintainer or authenticated user with configuration rights supplies a specially crafted release notes configuration file containing deeply nested YAML structures, the YAML parser on the server encounters recursive depth issues. As the parser attempts to traverse and evaluate the exponentially nested nodes, it consumes excessive CPU cycles and memory resources. This resource exhaustion leads to severe performance degradation or complete service unresponsiveness across the affected GitHub Enterprise Server node, impacting other hosted repositories and users. The flaw stems from insufficient recursion limits and depth validation within the YAML configuration ingestion engine used during release generation. Because release notes parsing occurs automatically upon certain release actions or configuration validations, an authenticated actor can trigger this condition repeatedly to sustain a denial-of-service state against the instance. Remediation requires updating the server software to versions where strict parsing recursion bounds and sanitization checks are enforced.
DailyCVE Form:
Platform: GitHub Enterprise Server
Version: Prior to 3.22
Vulnerability: Denial of Service
Severity: Medium level risk
Date: July 17 2026
Prediction: Patch released already
What Undercode Say:
Check GitHub Enterprise Server version
ghe-version
Inspect release notes configuration files for nested YAML
grep -rn "release_notes:" .github/
Test YAML parsing depth limits safely in staging
python3 -c "import yaml; yaml.safe_load(open('release-notes.yml'))"
Exploit: (Educational Purposes!)
Conceptual demonstration of generating deeply nested YAML for testing parser resilience
def create_nested_yaml(depth):
return "a:\n" + "".join([f" {' ' i}b:\n" for i in range(depth)])
payload = create_nested_yaml(10000)
with open("malicious_release_notes.yml", "w") as f:
f.write(payload)
Protection:
Upgrade GitHub Enterprise Server to patched versions (3.22, 3.21.3, 3.20.5, 3.19.9, 3.18.12, 3.17.18 or later).
Implement strict validation and depth limits on user-supplied YAML configuration files.
Restrict repository configuration file modification permissions to trusted administrative roles only.
Impact:
Service disruption and application unresponsiveness on GitHub Enterprise Server instances.
Exhaustion of server CPU and memory resources leading to potential node crashes.
Temporary denial of access for developers relying on the affected instance for CI/CD and source control.
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Sources:
Reported By: github.com
Extra Source Hub:
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