CVE-2026-91987

MEDIUMPre-NVD 6.56.5—
EchelonGraph scoreHIGH confidence

Score 6.5 from GitHub Security Advisory (severity: HIGH) published 2026-09-15. a secondary CVSS source baseline 6.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 4 sources updated this week
6.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.5Exploit: None knownExposed: 0

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

atomic-agents-stack before 1.1.0 contains a cost-guardrail bypass in the _estimate_batch_cost function that returns zero cost for unknown models not in the pricing table. Attackers can configure deployments with unknown model identifiers to bypass daily cost caps and exceed budget limits in parallel batch operations.

CVSS v3
6.5
EG Score
6.5(high)
EG Risk
29(Track)
EG Risk 29/100SSVC: 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
Severity65% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
31%
KEV
Not listed

Published

September 15, 2026

Last Modified

September 17, 2026

Advisory Details (2)

Auto-updated Sep 15, 2026
Patch available. Sources: github.
generic

atomic-agents-stack before 1.1.0 Cost Guardrail Bypass via Unknown Model | Advisories | VulnCheck

https://www.vulncheck.com/advisories/atomic-agents-stack-before-1.1.0-cost-guardrail-bypass-via-unknown-model
github Patch Available

Parallel helper/delegate batch reserves $0 for models absent from the pricing table, bypassing the cost-cap fan-out guard · Advisory · dep0we/atomic-agents-stack · GitHub

https://github.com/dep0we/atomic-agents-stack/security/advisories/GHSA-j659-8xh6-5pq5

Vendor Advisories for CVE-2026-91987(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)
PyPI(1)
PackageVulnerable rangeFixed inDependents
atomic-agents-stack1.0.01.1.0—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 20× in last 7d / 20× 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. 2026-09-20 20:16 UTCEPSS rescore
  2. 2026-09-20 12:04 UTCEG score recompute
  3. 2026-09-20 12:04 UTCGHSA enrichment
  4. 2026-09-19 14:04 UTCEG score recompute
  5. 2026-09-19 14:04 UTCGHSA enrichment
  6. 2026-09-18 19:28 UTCEPSS rescore
  7. 2026-09-18 16:08 UTCEG score recompute
  8. 2026-09-18 16:08 UTCGHSA enrichment
  9. 2026-09-17 19:32 UTCEPSS rescore
  10. 2026-09-17 18:08 UTCEG score recompute
  11. 2026-09-17 18:08 UTCGHSA enrichment
  12. 2026-09-17 15:29 UTCEG score recompute
  13. 2026-09-17 15:29 UTCGHSA enrichment
  14. 2026-09-17 12:23 UTCGHSA enrichment
  15. 2026-09-16 14:28 UTCEG score recompute
  16. 2026-09-16 14:28 UTCGHSA enrichment
  17. 2026-09-16 14:09 UTCEPSS rescore
  18. 2026-09-15 16:32 UTCEG score recompute
  19. 2026-09-15 15:23 UTCEG score recompute
  20. 2026-09-15 15:22 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-91987?
CVE-2026-91987 is a medium vulnerability published on September 15, 2026. atomic-agents-stack before 1.1.0 contains a cost-guardrail bypass in the estimatebatch_cost function that returns zero cost for unknown models not in the pricing table. Attackers can configure deployments with unknown model identifiers to bypass daily cost caps and exceed budget limits in parallel…
When was CVE-2026-91987 disclosed?
CVE-2026-91987 was first published in the National Vulnerability Database on September 15, 2026, with the most recent update on September 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-91987 actively exploited?
CVE-2026-91987 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 69.2% of all scored CVEs.
What is the CVSS score of CVE-2026-91987?
CVE-2026-91987 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2026-91987?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-91987, 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-2026-91987

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