Executive brief
The yaml JavaScript library is vulnerable to a denial-of-service condition when parsing YAML documents with deeply nested collections. An attacker can supply a small malicious YAML payload (as small as 2–10 KB) that triggers a stack overflow, causing the application to throw an unhandled exception and potentially crash. Applications that only expect YAML-specific errors may fail to catch this exception type, leading to service disruption.
Technical details
The vulnerability exists in the node composition/resolution phase of yaml's parser, which uses recursive function calls without depth bounds. While the CST (Concrete Syntax Tree) phase uses iterative stack-based processing and is unaffected, the compose/resolve phase recursively processes nested nodes. Flow sequences are particularly efficient for exploitation, requiring only 2 bytes per nesting level (one `[` and one `]`). On typical Node.js environments with default stack sizes, approximately 1,000–5,000 levels of nesting (2–10 KB input) exhaust the call stack and trigger a RangeError. The exception is not a YAMLParseError, so applications that selectively catch only YAML-specific errors will encounter an unexpected exception type. All three public parsing APIs are affected: `YAML.parse()`, `YAML.parseDocument()`, and `YAML.parseAllDocuments()`. Patches addressing this issue were released in versions 1.10.3 and 2.8.3, which catch the stack overflow and convert it to a YAMLParseError with code `RESOURCE_EXHAUSTION`.
Affected products
- eemeli yaml 1.0.0 through 1.10.2, 2.0.0 through 2.8.2
Timeline
- 2026-03-25: disclosed: Security advisory published on GitHub
- 2026-03-21: patched: Fix committed (v1.10.3 and v2.8.3 released on March 21, 2026)