CVE-2026-82404

HIGHPre-NVD 8.38.3—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 8.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4%, top 66% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
8.3EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 8.3Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

TOON is a compact, human-readable serialization of JSON data for LLM prompts. Prior to 2.3.1, decoding attacker-controlled TOON with a __proto__, constructor, or prototype key wrote through the object prototype chain instead of creating an own property, polluting Object.prototype for the runtime. In packages/toon/src/decode/expand.ts, the expandPaths: 'safe' path and insertPathSafe function made dotted keys such as a.__proto__.x the strongest vector, while plain nested objects, tabular rows, quoted keys, and streaming decode were also affected. The encoder also dropped own __proto__ properties and could invoke an inherited setter during normalization. Services that decode untrusted TOON could experience denial of service or, when a suitable downstream gadget is present, remote code execution. This issue is fixed in version 2.3.1.

CVSS v3
8.3
EG Score
8.3(medium)
EG Risk
53(Track)
EG Risk 53/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity83% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
34%
KEV
Not listed

Published

September 2, 2026

Last Modified

September 9, 2026

Advisory Details (4)

Auto-updated Sep 2, 2026
Patch available. Sources: github, github_pr, github_commit, github_release.
github_release Patch Available

v2.3.1

Patch available: toon-format/toon v2.3.1

https://github.com/toon-format/toon/releases/tag/v2.3.1
github_commit Patch Available

commit 94a2b7560b2b (toon-format/toon)

Patch available: toon-format/toon v2.3.1 (contains commit 94a2b7560b2b)

https://github.com/toon-format/toon/commit/94a2b7560b2b5ed903a4d466a3bce8b13daa2660
github_pr Patch Available

fix: harden encode and decode against prototype pollution

Patch available: toon-format/toon v2.3.1 (PR #316 merged 2026-07-15)

https://github.com/toon-format/toon/pull/316
github Patch Available

Prototype pollution when decoding untrusted TOON input · Advisory · toon-format/toon · GitHub

https://github.com/toon-format/toon/security/advisories/GHSA-p95v-992w-h6c3

Vendor Advisories for CVE-2026-82404(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(1 across 1 ecosystem)
npm(1)
PackageVulnerable rangeFixed inDependents
@toon-format/toon—2.3.1—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 13× in last 7d / 33× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-19 16:01 UTCEG score recompute
  2. 2026-09-19 02:44 UTCEG score recompute
  3. 2026-09-18 19:28 UTCEPSS rescore
  4. 2026-09-18 00:48 UTCEG score recompute
  5. 2026-09-16 22:51 UTCEG score recompute
  6. 2026-09-16 14:08 UTCEPSS rescore
  7. 2026-09-16 09:52 UTCEG score recompute
  8. 2026-09-16 05:15 UTCEPSS rescore
  9. 2026-09-15 07:22 UTCEG score recompute
  10. 2026-09-15 03:12 UTCEPSS rescore
  11. 2026-09-15 03:12 UTCEPSS rescore
  12. 2026-09-14 04:57 UTCEG score recompute
  13. 2026-09-13 03:01 UTCEG score recompute
  14. 2026-09-12 01:04 UTCEG score recompute
  15. 2026-09-11 14:53 UTCEPSS rescore
  16. 2026-09-11 14:53 UTCEPSS rescore
  17. 2026-09-11 12:05 UTCEG score recompute
  18. 2026-09-10 10:09 UTCEG score recompute
  19. 2026-09-08 23:11 UTCEG score recompute
  20. 2026-09-08 22:01 UTCEPSS rescore
  21. 2026-09-07 16:54 UTCEG score recompute
  22. 2026-09-06 14:57 UTCEG score recompute
  23. 2026-09-06 13:48 UTCEPSS rescore
  24. 2026-09-06 01:58 UTCEG score recompute
  25. 2026-09-05 15:31 UTCEPSS rescore
Show 8 more
  1. 2026-09-05 00:02 UTCEG score recompute
  2. 2026-09-04 11:04 UTCEG score recompute
  3. 2026-09-04 05:07 UTCEPSS rescore
  4. 2026-09-02 19:31 UTCEG score recompute
  5. 2026-09-02 19:12 UTCEG score recompute
  6. 2026-09-02 17:35 UTCEG score recompute
  7. 2026-09-02 16:46 UTCEG score recompute
  8. 2026-09-02 16:45 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-82404?
CVE-2026-82404 is a high vulnerability published on September 2, 2026. TOON is a compact, human-readable serialization of JSON data for LLM prompts. Prior to 2.3.1, decoding attacker-controlled TOON with a proto, constructor, or prototype key wrote through the object prototype chain instead of creating an own property, polluting Object.prototype for the runtime. In…
When was CVE-2026-82404 disclosed?
CVE-2026-82404 was first published in the National Vulnerability Database on September 2, 2026, with the most recent update on September 9, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-82404 actively exploited?
CVE-2026-82404 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 66.2% of all scored CVEs.
What is the CVSS score of CVE-2026-82404?
CVE-2026-82404 has a CVSS v3 base score of 8.3 (NVD).
How do I remediate CVE-2026-82404?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-82404, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-82404

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