CVE-2026-39861

CRITICALNVD 10.010.0—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 10.0 under NVD CVSS v3. EPSS exploit probability: 0.5%, top 59% 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, nvd
10.0
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 1%CVSS: 10.0Exploit: NoneExposed: 0

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

Claude Code is an agentic coding tool. Prior to version 2.1.64, Claude Code's sandbox did not prevent sandboxed processes from creating symlinks pointing to locations outside the workspace. When Claude Code subsequently wrote to a path within such a symlink, its unsandboxed process followed the symlink and wrote to the target location outside the workspace without prompting the user for confirmation. This allowed a sandbox escape where neither the sandboxed command nor the unsandboxed app could independently write outside the workspace, but their combination could write to arbitrary locations, potentially leading to code execution outside the sandbox. Reliably exploiting this required the ability to add untrusted content into a Claude Code context window to trigger sandboxed code execution via prompt injection. Users on standard Claude Code auto-update have received this fix automatically. Users performing manual updates are advised to update to version 2.1.64 or later.

CVSS v3
10.0
EG Score
10.0(medium)
EG Risk
45(Track)
EG Risk 45/100SSVC: 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
Severity100% × 45%
Exploitation1% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
40.9%
KEV
Not listed

Published

April 21, 2026

Last Modified

April 23, 2026

Advisory Details (1)

Auto-updated Jul 16, 2026
Patch available. Sources: github.
github Patch Available

Sandbox Escape via Symlink Following Allows Arbitrary File Write Outside Workspace · Advisory · anthropics/claude-code · GitHub

https://github.com/anthropics/claude-code/security/advisories/GHSA-vp62-r36r-9xqp

Affected Packages

(1 across 1 ecosystem)
npm(1)
PackageVulnerable rangeFixed inDependents
@anthropic-ai/claude-code—2.1.64—

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 8× in last 7d / 35× 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. 2026-07-23 03:10 UTCEG score recompute
  2. 2026-07-22 14:08 UTCEPSS rescore
  3. 2026-07-21 15:24 UTCEPSS rescore
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  1. 2026-07-01 15:06 UTCEPSS rescore
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  65. 2026-05-20 11:22 UTCEPSS rescore
  66. 2026-05-18 22:17 UTCEG score recompute

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-39861?
CVE-2026-39861 is a critical vulnerability published on April 21, 2026. Claude Code is an agentic coding tool. Prior to version 2.1.64, Claude Code's sandbox did not prevent sandboxed processes from creating symlinks pointing to locations outside the workspace. When Claude Code subsequently wrote to a path within such a symlink, its unsandboxed process followed the…
When was CVE-2026-39861 disclosed?
CVE-2026-39861 was first published in the National Vulnerability Database on April 21, 2026, with the most recent update on April 23, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-39861 actively exploited?
CVE-2026-39861 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 40.9% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-39861?
CVE-2026-39861 has a CVSS v3 base score of 10.0 (NVD).
How do I remediate CVE-2026-39861?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-39861, 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.

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