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Site Isolation Bypass in Google Chrome Extensions

IdentifiersCVE-2026-12457CWE-20

CVE-2026-12457 is a high-severity vulnerability in Google Chrome Extensions, affecting Chrome prior to 149.0.7827.155. The issue is described as an inappropriate implementation / insufficient data validation flaw in the Extensions component. According to the provided advisory, a remote attacker who had already compromised the renderer process could use a crafted HTML page to bypass Chrome site isolation protections. The vulnerability therefore does not appear to be an initial code-execution bug by itself; rather, it is a post-compromise browser security boundary bypass that weakens isolation between sites once renderer compromise has been achieved.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation allows an attacker who already controls or has compromised a renderer process to bypass Chrome's site isolation boundary. This can weaken origin and process separation guarantees, potentially enabling cross-site access that should normally be blocked, facilitating sensitive information exposure across site boundaries and making exploit chains more effective. The vulnerability is therefore best characterized as a security restriction bypass that can contribute to sandbox-escape or post-exploitation browser attack chains.

Mitigation

If you can’t patch tonight, do this now.

No specific workaround or temporary mitigation is provided in the supplied advisories beyond applying the vendor updates. As a defense-in-depth measure, reducing exposure to renderer-compromise chains through prompt browser patching, endpoint protections, and browser isolation controls may reduce practical exploitation risk, but the primary mitigation is to update affected browsers.

Remediation

Patch, then assume compromise.

Upgrade Google Chrome to version 149.0.7827.155 or later. For Chromium on Debian, upgrade to the vendor-fixed packages identified in the advisory: 149.0.7827.155-1~deb13u1 for Debian stable (trixie) or 149.0.7827.155-1~deb12u1 for Debian oldstable (bookworm). For Microsoft Edge (Chromium-based), upgrade to version 149.0.4022.80 or later, which incorporates the Chromium fix.
PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType
GoogleChromeapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

6 SOURCESView more in app
What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.
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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity1

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES
MITRE CVE
cve.org · CVE-2026-12457
NVD
nvd.nist.gov/vuln/detail/CVE-2026-12457
MITRE CWE · CWE-20
cwe.mitre.org