Prototype pollution via unsafe TOML object merging
Published Aug 14, 2025 · Updated Aug 14, 2025
Prototype pollution in @std/toml before 1.0.9 allows context-dependent attackers to alter inherited properties via crafted TOML. The TOML parser reduces parsed blocks into an ordinary object, while deepAssignTable and deepAssignTableArray follow proto table keys and merge nested data into Object.prototype. Reachability requires a Node.js or browser application to parse attacker-controlled TOML and contain a gadget that consumes a polluted property; the normal Deno runtime disables Object.proto.
Summary
What happened
Prototype pollution in @std/toml before 1.0.9 allows context-dependent attackers to alter inherited properties via crafted TOML. The TOML parser reduces parsed blocks into an ordinary object, while deepAssignTable and deepAssignTableArray follow proto table keys and merge nested data into Object.prototype. Reachability requires a Node.js or browser application to parse attacker-controlled TOML and contain a gadget that consumes a polluted property; the normal Deno runtime disables Object.proto.
The record
- CVE
- CVE-2025-55195
- Published
- Aug 14, 2025
- Updated
- Aug 14, 2025
- Vendor
- Deno Land Inc.
- Product
- Deno Standard Library
- Classifications
- CWE-1321, T1203
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 14, 2025CVE publishedPublication date reported by the CVE source.
- Aug 14, 2025Record 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=< 1.0.9
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
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
- GHSA-crjp-8r9q-2j9r Node.js proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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