Code execution via !js eval
Published Aug 20, 2026 · Updated Aug 20, 2026
Arbitrary code execution in CustomerGauge @cgauge/yaml 0.27.0 and earlier allows attackers to run JavaScript via !js tags. In yaml/src/parser.ts, the jsType custom tag handler accepts any scalar string and passes it directly to eval() in construct(), and schema() adds that type to the default parser schema for every load(). Exposure requires an application to parse attacker-controlled YAML with this library, after which injected code runs with the hosting Node.js process's filesystem, network, environment, and subprocess privileges.
Summary
What happened
Arbitrary code execution in CustomerGauge @cgauge/yaml 0.27.0 and earlier allows attackers to run JavaScript via !js tags. In yaml/src/parser.ts, the jsType custom tag handler accepts any scalar string and passes it directly to eval() in construct(), and schema() adds that type to the default parser schema for every load(). Exposure requires an application to parse attacker-controlled YAML with this library, after which injected code runs with the hosting Node.js process's filesystem, network, environment, and subprocess privileges.
The record
- CVE
- CVE-2026-76833
- Published
- Aug 20, 2026
- Updated
- Aug 20, 2026
- Vendor
- CustomerGauge
- Product
- @cgauge/yaml
- Classifications
- CWE-95, T1059.007
- Attack vector
- local
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 20, 2026CVE publishedPublication date reported by the CVE source.
- Aug 20, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <=0.27.0
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- cgauge-yaml-disclosure.md proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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