EUVD-2026-45188
GHSA-x3vv-vhr6-576j
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-reachable, low complexity, requires authenticated low-privilege user; scope change (S:C) because instance-wide availability impact extends beyond the release notes component.
Primary rating from Vendor (GitHub_P).
CVSS VectorVendor: GitHub_P
Lifecycle Timeline
1DescriptionCVE.org
A denial of service vulnerability was identified in GitHub Enterprise Server that allowed an authenticated user to cause service disruption by supplying a repository release notes configuration file containing deeply nested YAML. When release notes were generated, the configuration file was parsed without a nesting depth limit, causing excessive resource consumption that could render the instance unresponsive. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.22 and was fixed in versions 3.17.18, 3.18.12, 3.19.9, 3.20.5, and 3.21.3. This vulnerability was reported via the GitHub Bug Bounty program.
AnalysisAI
GitHub Enterprise Server (all versions prior to 3.22) is vulnerable to authenticated denial of service via unbounded YAML parsing depth in release notes configuration files. An authenticated user with repository access can craft a release notes configuration file containing arbitrarily deeply nested YAML structures; when release note generation is triggered, the YAML parser processes the nesting without any depth limit, causing excessive CPU and memory consumption that can render the entire GHES instance unresponsive. No public exploit has been identified at time of analysis, and this was responsibly disclosed through the GitHub Bug Bounty program.
Technical ContextAI
GitHub Enterprise Server (CPE: cpe:2.3:a:github:enterprise_server:*:*:*:*:*:*:*:*) includes a release notes generation feature that reads a repository-supplied YAML configuration file. The root cause is CWE-770 (Allocation of Resources Without Limits or Throttling): the YAML parser invoked during release note generation applies no maximum recursion depth or nesting limit, making it susceptible to deeply nested YAML structures (sometimes called YAML bombs or YAML stack exhaustion attacks). When processing such a file, the parser recursively allocates stack frames and heap memory proportional to nesting depth, eventually exhausting available resources. This class of vulnerability is distinct from a YAML alias expansion attack (Billion Laughs) - the mechanism here is depth-induced stack/heap exhaustion rather than anchor/alias multiplication, but the availability impact is equivalent.
RemediationAI
The primary remediation is to upgrade to a patched release: 3.17.18, 3.18.12, 3.19.9, 3.20.5, or 3.21.3, depending on the currently deployed release train. Release notes for each patch are available at the GitHub documentation URLs listed under affected products. If an immediate upgrade is not feasible, consider restricting repository write access (which controls who can push release notes configuration files) to trusted users only, reducing the insider threat surface. Additionally, monitoring for abnormal GHES process CPU or memory spikes during release note generation activity can provide early warning of exploitation attempts. There is no known configuration toggle to disable the release notes YAML parser independently without disabling the feature entirely - disabling the release notes generation feature in repositories would eliminate the attack surface but at the cost of losing release notes functionality. No workaround preserves full functionality while preventing exploitation.
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External POC / Exploit Code
Leaving vuln.today