CVE-2026-87491: Google Chromium V8 Out of Bounds Write Vulnerability

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Yes, if you run Google Chromium V8. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-09-09, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-09-23; treat that as the outer limit, not the target.
• EPSS 3.1%, percentile 88: FIRST’s model estimates a 3.1% chance of exploitation activity in the next 30 days, higher than 88% of all scored CVEs (elevated). EPSS is a probability, not a verdict.
• Needs a user to click or open something. Phishing makes that realistic, but it is not wormable.
• Editorial verdict: Check exposure. Chrome V8 Zero-Days CVE-2026-85046 and CVE-2026-87491 — Both were exploited zero-days, but Chrome and Edge fixed them in early September and auto-update has had six weeks to deliver the fix; the job now is finding browsers that did not update, not a scramble.

What it is

Out of bounds write in V8 in Google Chrome prior to 153.0.8010.36 allowed a remote attacker to execute arbitrary code inside the sandbox via a crafted HTML page. (Chromium security severity: Medium)

CISA’s summary

Google Chromium V8 contains an out of bounds write vulnerability that allows a remote attacker to execute arbitrary code inside the sandbox via a crafted HTML page. This vulnerability could affect multiple web browsers that utilize Chromium, including, but not limited to, Google Chrome, Microsoft Edge, and Opera.

Weakness type: CWE-787.

Product: Google Chromium V8 · Assigned by: Chrome · Published: 2026-09-09

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: required (a user must click/open something)
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: added 2026-09-09; federal due date 2026-09-23. Known ransomware use: Unknown.
• CISA required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
• CISA SSVC assessment: exploitation active, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 3.14% probability of exploitation activity in the next 30 days; percentile 88.

Timeline

• 2026-09-03 — erroneo.us brief: Chrome V8 Zero-Days CVE-2026-85046 and CVE-2026-87491
• 2026-09-09 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2026-09-09 — CVE record published by Chrome
• 2026-09-21 — CVE record last updated
• 2026-09-23 — CISA remediation deadline for US federal agencies

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. Listed in CISA KEV notes (chromereleases.googleblog.com) chromereleases.googleblog.com

Vulnerability records

1. CVE.org record CVE-2026-87491 cve.org
2. NVD entry CVE-2026-87491 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov
2. Listed in CISA KEV notes (cisa.gov) cisa.gov
3. Listed in CISA KEV notes (cisa.gov) cisa.gov

Other references from the CVE record and advisory

1. issues.chromium.org issues.chromium.org

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