PUBLIC-EVIDENCE AI SECURITY CASE STUDY

Cursor Agent JSON schema fetch from an injected file

The researcher and Cursor advisory describe a compromised agent writing a JSON schema URL; Cursor automatically made the external GET without user confirmation. Data exfiltration through that GET was a potential impact, not an observed stolen-secret event.

Agentic / MCP SystemTier 3Indicative ERS 3.7 (1.1–6.4)Evidence source date 2025-06-11

Use case sources

Source reports and analysis supporting this case are listed below. AITBM interpretation and any indicative scoring are derived from this public evidence.

Linked library records

Independent products or attack paths are assessed separately. A combined report receives no aggregate score.

Original report record: IDEsaster Shows How Agent File Writes Can Activate Trusted IDE Features.

The researcher and Cursor advisory describe a compromised agent writing a JSON schema URL; Cursor automatically made the external GET without user confirmation. Data exfiltration through that GET was a potential impact, not an observed stolen-secret event.

ASSESSED SYSTEM

Representative Cursor before 0.51.0, default JSON schema download enabled; only the product-specific pre-fix path in the advisory is assessed.

OUT OF SCOPE

Compromised agent or successful prompt injection is a precondition; no confirmed victim secret theft. Patched releases, unrelated editor products, and victim exploitation are outside scope.

Architecture: Agentic / MCP System (decision tree Q2) — Q2 applies because the coding agent reads attacker-controlled task context and uses its own file/search tools to change persistent IDE state or trigger an IDE background action. No multi-agent coordination is evidenced. Tier 3: Tier 3 representative developer or internal AI workflow scenario; the original source does not establish every operator tier.

Documented attack or failure path

  1. An attacker influenced an AI coding agent through a prompt or untrusted content in the documented configuration.
  2. The agent used its ordinary file or search tool to cross the specific IDE boundary described in the advisory.
  3. The IDE or agent then performed the external read, network fetch, settings change, or code execution consequence reported for this path.

Observed controls and bounded outcomes

Positive credit is given only where the record directly demonstrates a control operating. Recommended or merely presumed controls receive no positive scoring credit.

  • The maintainer fixed this specified path in the published patched release; that later release is not credited to the pre-fix scenario.

Layer 1 — Intrinsic Vulnerability Profile

Each sub-metric is placed on its five-level rubric by the evidence quoted beside it. Missing applicable evidence remains unknown. The displayed midpoint and interval are scenario values, not inferred control performance.

Sub-metricScoreRubric basisEvidence
Robustness (Ro) — scenario interval 0.00–1.00 (midpoint 0.50), Tier 3 MVT 0.40 indeterminate
Fairness (Fa) — scenario interval 0.00–1.00 (midpoint 0.50), Tier 3 MVT 0.45 indeterminate
Transparency (Tr) — scenario interval 0.00–1.00 (midpoint 0.50), Tier 3 MVT 0.45 indeterminate
Privacy (Pr) — scenario interval 0.00–1.00 (midpoint 0.50), Tier 3 MVT 0.50 indeterminate
Containment (Cn) — scenario interval 0.00–0.91 (midpoint 0.46), Tier 3 MVT 0.50 indeterminate
Cn-1Scope Enforcement0.00w 0.09An agent-controlled file caused an out-of-scope network request with no effective gate; the observed GET satisfies Cn-1 0.00.The default schema fetch followed a model-influenced JSON write to an arbitrary external URL without a per-request authorization gate.source: primary report

Unknown, not N/A: 25 applicable sub-metrics lack admissible public evidence. The lower, midpoint, and upper scenarios evaluate each at 0.00, 0.50, and 1.00 respectively; no weight is redistributed merely because evidence is missing.

Layer 2 — Operational Risk Posture

DimensionScoreJustification
AaAutonomy Amplification0.75w 0.20Representative activity level for the documented bounded AI path; deployment-specific autonomy was not measured.
AsAttack Surface Exposure0.50w 0.25Representative exposure of the documented entry path; this is a scenario assumption and not a census of all operators.
CpCascade Potential1.00w 0.30No verified System Dependency Graph or DGC is published, so framework worst-case Cp default applies.GDCP: worst-case default — no verified dependency graph published elevated
RfRemediation Feasibility0.25w 0.25A specific patch or configuration change is documented; repair feasibility is an inferred representative scenario, not measured recovery time.

Nelevated = 1 (dimensions strictly above 0.75) → CRM = 1.00.

Layer 3 — Public-evidence confidence diagnostic

ComponentScoreBasis
Pc — Public provenance evidence0.25Minimal public provenance identifies the affected path but supplies no operator assessment pack, signed configuration inventory, or repeated metric battery.
Ec — Public evaluation coverage0.03coverage 0.04 (1 of 26 applicable sub-metrics) × independence 0.80 × fidelity 0.95. No Full, Standard, or Lite pathway is claimed for a retrospective article.
Tf — Public-evidence freshness0.02Evidence dated 2025-06-11; age 494 days on the workpaper reference date. Components: T_containment 0.02 · T_calendar 0.15 · C_monitor 0.70. Binding term: T_containment. Evidence reference is 2026-10-18, 494 days after earliest substantive public evidence (2025-06-11). C_monitor uses the conservative Tier 3 public-evidence default because usable monitoring-coverage evidence is unavailable; it does not assert no deployment telemetry. No C_event cap is asserted from research or an advisory without a dated victim incident. No generic C_evidence cap is assigned from missing public inputs. Indicative ERS uses normalized ACI = 1.00 for comparison only.

Public-evidence ACI = (Pc × Ec × Tf)1/3 = 0.06 — diagnostic status: Invalid as assessment-of-record evidence. It describes the evidence available to this case study, not the assurance of the underlying system, and is not inserted into the normalized-assurance scenario ERS.

Indicative ERS — normalized-assurance scenario

Worp · ORP0.20(0.75) + 0.25(0.50) + 0.30(1.00) + 0.25(0.25) = 0.637
CRMNelevated = 1 → 1.00
ORPeffective0.637 × 1.00 = 0.637
Wivp · IVP midpoint0.20(0.50) + 0.15(0.50) + 0.20(0.50) + 0.25(0.50) + 0.20(0.46) = 0.491
IVP mitigation0.15 + 0.85(1 − 0.491) = 0.583
Scenario assuranceACI fixed at 1.000 for cross-case comparison; public-evidence ACI 0.056 is diagnostic only
Indicative ERS midpointmin(10, 0.637 × 0.583 × 1/1.000 × 10) = 3.7
Unknown-input interval1.1–6.4; 25 unknown applicable sub-metrics set to 1.00 / 0.00 at the bounds

Published CVSS beside indicative ERS

Each published CVSS record is shown exactly as its scorer published it, one per vulnerability record, with the version, metric group and vector when stated, plus its source and access date. Records are never combined or inferred from a CVE's existence.

INDICATIVE ERS · NORMALIZED-ASSURANCE SCENARIO

3.7 midpoint, interval 1.1–6.4; Low-Moderate scenario band; ACI fixed at 1.00. The published CVSS records do not enter this calculation.

PUBLISHED CVSS · 1 record

CVE-2025-49150 CVSS 3.1 Base 5.9 Medium

Published score5.9
CVSS version3.1
Metric groupBase
SeverityMedium
VectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Scored byGitHub maintainer CNA
Source recordhttps://github.com/cursor/cursor/security/advisories/GHSA-9h3v-h59j-v6rj (accessed 2026-10-18)
Affected componentCursor before 0.51.0, default JSON schema download enabled
Scope noteThe vendor advisory CVE covers the exact product and configuration of this representative agent path.

CVSS describes an individual vulnerability as its scorer published it. Indicative ERS describes the assessed AI deployment under the normalized-assurance scenario, so the two values are not direct equivalents and neither replaces the other.

WHAT THIS CASE TEACHES

The default schema fetch followed a model-influenced JSON write to an arbitrary external URL without a per-request authorization gate. The AITBM anchor applies only to the stated product and configuration.

Sources: Vendor or maintainer advisory — CVE-2025-49150 · Original IDEsaster researcher case study (2025-12-06)

AITBM sub-metrics referenced