CVE-2026-96620

CRITICALPre-NVD 9.29.2
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

This critical-severity CVE scores 9.2 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.6% (46th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from a secondary CVSS source
Sources: EPSS, a secondary CVSS source
Trending — 3 sources updated this week
9.2EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.6%CVSS: 9.2Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Claude Agent SDK is a Python SDK for Claude Code. Prior to 0.2.121, the resume option is passed to the Claude CLI as a separate token without validation, so a dash-leading value is parsed as an independent CLI flag. An attacker can inject the --mcp-config flag to define a stdio MCP server, causing arbitrary command execution at CLI startup outside the SDK permission controls. The issue is exploitable when an application passes untrusted input as the session ID to resume. This issue is fixed in version 0.2.121.

CVSS v3
9.2
EG Score
9.2CRITICALmedium confidence
EG Risk
57
EG Risk 57/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity92% × 45%
Impact severity (EG Severity): CVSS 9.2 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.6% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability100% × 15%
CISA's SSVC Automatable value: yes (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Attend at high (mission-essential systems).
Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.6%
EPSS %ILE
46th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (9.2): severity, escalated by confirmed exploitation. This CVE's 9.2 is its impact severity (EG Severity), not escalated.

EG Severity
9.2 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.a secondary CVSS source · CVSS v3.0 or v3.1
EG Likelihood
0.6% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-21). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at low or medium mission impact; Attend at high (mission-essential systems).CISA BOD 26-04: 3 days if the affected system is publicly exposed; 60 days if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)3 days if the affected system is publicly exposed; 60 days if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

October 16, 2026

Last Modified

October 21, 2026

Advisory Details (4)

Auto-updated Oct 16, 2026
Patch available. Sources: github, github_pr, github_commit, github_release.
GitHub release Patch Available

v0.2.121

Patch available: anthropics/claude-agent-sdk-python v0.2.121

https://github.com/anthropics/claude-agent-sdk-python/releases/tag/v0.2.121
GitHub commit Patch Available

commit 347a1cb88d76 (anthropics/claude-agent-sdk-python)

Patch available: anthropics/claude-agent-sdk-python v0.2.138 (contains commit 347a1cb88d76)

https://github.com/anthropics/claude-agent-sdk-python/commit/347a1cb88d7652199399db1b7f914e0a459a6662
GitHub pull request Patch Available

Pass --resume and --session-id as a single argv token

Patch available: anthropics/claude-agent-sdk-python v0.2.138 (PR #1123 merged 2026-07-16)

https://github.com/anthropics/claude-agent-sdk-python/pull/1123
GitHub advisoryMentions a patch (unverified)

Argument Injection via resume Option Allows Arbitrary Command Execution · Advisory · anthropics/claude-agent-sdk-python · GitHub

https://github.com/anthropics/claude-agent-sdk-python/security/advisories/GHSA-h4mw-j7qp-8mwm

Vendor Advisories for CVE-2026-96620(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 rangeFix by version rangeDependents
claude-agent-sdk0.0.23 ... 0.2.99 (105 versions)
  • every version up to 0.2.121: fixed in 0.2.121
—

Weakness Classification(3)

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

Data Freshness Timeline

(refreshed 16× in last 7d / 16× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

  1. 2026-10-21 22:28 UTCEG score recompute
  2. 2026-10-21 21:42 UTCEG score recompute
  3. 2026-10-21 18:55 UTCEG score recompute
  4. 2026-10-21 16:34 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  5. 2026-10-20 16:46 UTCEG score recompute
  6. 2026-10-20 16:34 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  7. 2026-10-19 21:29 UTCEG score recompute
  8. 2026-10-19 16:33 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  9. 2026-10-19 00:50 UTCEG score recompute
  10. 2026-10-18 16:33 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  11. 2026-10-18 02:57 UTCEG score recompute
  12. 2026-10-17 22:39 UTCEG score recompute
  13. 2026-10-17 16:35 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  14. 2026-10-16 20:27 UTCEG score recompute
  15. 2026-10-16 19:54 UTCEG score recomputeFirst assessed: 9.2 CRITICAL
  16. 2026-10-16 19:52 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-96620?
CVE-2026-96620 is a critical-severity vulnerability; its CVE record was published on October 16, 2026. Claude Agent SDK is a Python SDK for Claude Code. Prior to 0.2.121, the resume option is passed to the Claude CLI as a separate token without validation, so a dash-leading value is parsed as an independent CLI flag. An attacker can inject the --mcp-config flag to define a stdio MCP server, causing…
When was the CVE record for CVE-2026-96620 published?
The CVE record for CVE-2026-96620 was published on October 16, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of October 21, 2026; the record at its source may have been updated since.
Is CVE-2026-96620 actively exploited?
CVE-2026-96620 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.6% probability of exploitation in the next 30 days (46th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-96620?
CVE-2026-96620 has a CVSS base score of 9.2 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-96620?
A fix for CVE-2026-96620 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-96620 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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