CVE-2026-79263

Executive Summary

CVE-2026-79263 is a race condition vulnerability in the Extensions component of Google Chrome, affecting versions prior to 152.0.7977.65. A remote attacker can exploit this flaw by delivering crafted network traffic to a victim, potentially achieving arbitrary code execution within the Chrome sandbox. Although Chromium classified this as a Low-severity issue, the NVD CVSS score of 8.1 (High) reflects the significant confidentiality, integrity, and availability impacts if the sandbox escape is chained with a separate renderer compromise. The vulnerability has a public PoC available, elevating the urgency for enterprise patch management teams despite the absence of CISA KEV listing.

Technical Analysis

The vulnerability exists in the Extensions component of Google Chrome and is classified as CWE-367 (Time-of-check Time-of-use Race Condition). This class of vulnerability arises when a program checks the state of a resource (time-of-check) and then uses that resource (time-of-use) without ensuring the state has not changed between the two operations. In the context of browser extensions, this typically involves a race between an asynchronous operation — such as a network request callback or an extension API invocation — and the state of an extension's internal data structures or permissions.

The NVD description indicates the attack vector is crafted network traffic. This suggests the race condition is triggered through network-delivered content that interacts with an extension's message-passing or network interception APIs. The NVD description does not provide function names, specific extension APIs, or code-level implementation details. However, attack mechanisms consistent with this description include:

• TOCTOU on extension storage or settings: An extension may read a configuration value (e.g., a remote content security policy or a list of allowed origins) and then act on it asynchronously. A crafted network response could modify that value between the check and the use, leading to unintended code execution.
• Race on extension service worker lifecycle: Extensions using service workers may have a race between the worker being terminated and a network event being processed. A crafted response could cause the worker to be re-instantiated with an altered environment.
• Race in native messaging bridge: If the extension uses native messaging, a race between the network-triggered message and the native host's response could allow improper data handling.

The Chromium security severity of Low suggests the exploitability in practice is constrained — likely requiring specific extension configurations or user interaction to set up the vulnerable state. However, the CVSS vector AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H indicates a high attack complexity — meaning the race must be reliably won by the attacker, but no privileges or user interaction are required, and the impact on the sandbox's host environment (Confidentiality, Integrity, Availability) is complete if successful.

Patch confidence is 2/4 (CLAIMED) — the fix is attributed only to the NVD, and no independent vendor confirmation or advisory details are available. The fixed version is 152.0.7977.65. No CVE data is provided regarding which specific patch commit addressed the flaw, and the affected version range is empty in the provided data (inferring all versions prior to 152.0.7977.65 are affected).

Exploitation Scenarios

No public PoC details are available; the attack chain below is inferred from the vulnerability class (race condition in Extensions) and the attack vector (network traffic).

Step 1 — Reconnaissance / Target Identification The attacker identifies victims running Chrome versions prior to 152.0.7977.65. The attacker must also identify a target environment where a vulnerable extension is installed and active. Reconnaissance techniques include:

• Detecting Chrome version via user-agent strings, client-side fingerprinting, or HTTP response heuristics.
• Identifying extension presence via web-accessible resources (extension IDs in URLs or known behavior patterns) or via timing side-channels.

Step 2 — Triggering the Vulnerability Class The attacker crafts malicious network traffic designed to hit the vulnerable code path in the Extensions component. Given CWE-367, the attacker must create a scenario where:

• The extension performs a check (e.g., validates a resource, reads a setting, or verifies a permission).
• The attacker's network response arrives between the check and the subsequent use of that checked value.
• The response mutates the state such that the extension proceeds with an invalid or attacker-controlled value.

This is delivered via a webpage the victim visits, or via an HTTP response injected into an existing connection (e.g., through a rogue proxy or network position).

Step 3 — Payload / Execution Method The attacker's crafted payload causes the extension to act on the mutated state, leading to arbitrary code execution. At the vulnerability-class level, the execution mechanism is:

• The extension interprets the attacker-modified data as executable code, a configuration directive, or a privileged API call.
• The extension executes this data within its own privileges (or passes it to the browser's native code), resulting in code execution inside the browser sandbox.

Because the NVD description states "execute arbitrary code inside the sandbox," the immediate execution is confined to the sandboxed renderer or extension process. A full system compromise would require a second, separate sandbox-escape vulnerability.

Step 4 — Post-Exploitation Impact

• Within the sandbox: The attacker gains code execution in the context of the extension and the renderer. This allows theft of extension-stored credentials, modification of web content, keylogging within the browser, and access to data available through extension permissions.
• Sandbox escape: If chained with a renderer sandbox escape (e.g., a separate Chrome Mojo or GPU vulnerability), the attacker achieves arbitrary code execution on the host OS with the privileges of the browser process. At this point, full host compromise — data exfiltration, persistence, lateral movement — is possible.

Note: No public PoC or exploit code is available, only a "Public" PoC status — indicating a proof-of-concept exists (perhaps a technical write-up or trigger PoC) but no functional exploit code is published. The attack chain is inferred from the vulnerability class.

Impact Assessment

• CVSS Score: 8.1 (High). The vector AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H indicates:

  • Attack Vector (Network): Remotely exploitable over network traffic.
  • Attack Complexity (High): The race condition must be reliably timed/won, requiring specific conditions or repeated attempts.
  • Privileges Required (None): No authentication or special privileges needed.
  • User Interaction (None): No user interaction required (mitigating factor that raises severity from the Chromium "Low" rating).
  • Scope (Unchanged): The compromise remains within the browser's security boundary (sandbox), though the impact within that boundary is complete.
  • C/I/A Impact (High): Full confidentiality, integrity, and availability within the sandbox.

• Affected Systems: All Chrome installations prior to 152.0.7977.65, where the user has extensions installed. Windows, macOS, and Linux variants are affected (the CVE data specifies no platform restriction). Enterprise environments with browser extension management are the highest-risk population due to centralized extension deployment.

• Blast Radius:

  • Direct: Compromise of browser sandbox, extension data theft, browser-level surveillance.
  • Extended: If chained with sandbox escape, full host compromise. The public PoC status suggests active attacker interest; the low EPSS score (0.00286) indicates low current exploitation prevalence, but this could change.

• Business Impact: Credential theft (browser-stored passwords), session hijacking, corporate data exfiltration via browser processes, loss of trust in endpoint security posture. Compliance implications if attacker gains access to regulated data.

Detection Guidance

The following rules target detection of traffic or behavior patterns consistent with exploitation of this race condition. Because the vulnerability is in the browser's extension handling of network traffic, detection is challenging at the network layer; host-based monitoring is likely more effective.

Sigma Rule

title: Chrome Extension Race Condition - Crafted Network Traffic Attempt
id: 8f3a2c9e-5d21-4b8a-9c7d-1e9a3b5c7f00
status: experimental
description: Detects Chrome processes receiving suspicious network responses that may indicate exploitation of CVE-2026-79263, a TOCTOU race condition in Chrome Extensions.
author: Valtersit Threat Intel
date: 2026/01/01
logsource:
  category: process_creation
  product: windows
detection:
  selection_chrome_network:
    Image|endswith: '\chrome.exe'
    CommandLine|contains:
      - '--disable-features'
      - '--enable-features'
  selection_suspicious_response:
    # Placeholder for any specific indicators from endpoint telemetry (e.g., unusual child processes, debugger flags)
    ParentImage|endswith: '\chrome.exe'
  condition: selection_chrome_network and selection_suspicious_response
falsepositives:
  - Legitimate Chrome enterprise policies using command-line switches
  - Normal browser operation
level: medium
tags:
  - attack.t1203
  - attack.execution

YARA Rule

rule CVE_2026_79263_Chrome_Extension_Race
{
    meta:
        author = "Valtersit Threat Intel"
        description = "Detects network payloads or extension files potentially crafted to exploit Chrome Extension TOCTOU race condition CVE-2026-79263"
        date = "2026-01-01"
        reference = "CVE-2026-79263"
        severity = "high"
    strings:
        $extension_marker = "chrome-extension://" ascii
        $race_pattern_1 = "race" ascii nocase
        $race_pattern_2 = "timeofcheck" ascii nocase
        $race_pattern_3 = "timeofuse" ascii nocase
        $network_trigger = "Content-Type: application/json" ascii
        $network_trigger2 = "Content-Type: text/event-stream" ascii
    condition:
        uint16(0) == 0x4D5A and // PE file (extension payload)
        ($extension_marker at any of them) and
        2 of ($race_pattern*) and
        (1 of ($network_trigger*) or 1 of ($section*))
}

rule CVE_2026_79263_Chrome_NetTraffic
{
    meta:
        author = "Valtersit Threat Intel"
        description = "Detects suspicious network traffic patterns (HTTP responses) targeting Chrome extensions, potentially exploiting CVE-2026-79263"
        date = "2026-01-01"
        severity = "medium"
    strings:
        $susp_hdr = "HTTP/1.1 200 OK" ascii
        $susp_ct = "Content-Type: application/octet-stream" ascii
        $ext_ref = "chrome-extension" ascii nocase
        $long_body = { 00 00 00 00 00 00 00 00 } // placeholder for large payload
    condition:
        $susp_hdr at 0 and $ext_ref and $susp_ct
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-79263 Chrome Extension Race Condition Exploit Attempt"; flow:established,to_client; content:"HTTP/1.1 200 OK"; content:"Content-Type:"; content:"chrome-extension"; nocase; content:"!|22|"; threshold:type both, track by_src, count 50, seconds 60; classtype:attempted-admin; sid:20260001; rev:1;)

Elastic Detection

sequence by process.entity_id with maxspan=10s
  [network where process.name == "chrome.exe" and 
   network.direction : "ingress" and 
   destination.port == 443 and 
   network.protocol == "http"]
  [process where process.name == "chrome.exe" and 
   event.type == "start" and 
   process.args : ("--renderer", "--extension-process")]

Splunk SPL Query

index=network sourcetype=stream:http dest_port=443 bytes>10000
| search uri=*chrome-extension* OR http_content_type=application/json
| stats count by src_ip, dest_ip, uri, _time
| where count > 50
| table _time, src_ip, dest_ip, uri, count
| sort - count

index=endpoint sourcetype=XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
| search EventCode=1 Image=*chrome.exe
| rex field=CommandLine "(?<feature_flags>--enable-features[^\s]*)"
| where feature_flags != ""
| stats count by Computer, User, Image, CommandLine
| sort - count

Wazuh OSSEC Rule

<group name="browser,">
  <rule id="100401" level="12">
    <decoded_as>json</decoded_as>
    <field name="event.module">network</field>
    <field name="network.protocol">http</field>
    <match>chrome-extension</match>
    <description>CVE-2026-79263: Suspicious network response targeting Chrome extension mechanism detected</description>
    <mitre>
      <id>T1203</id>
    </mitre>
    <group>attack.execution,</group>
  </rule>
  <rule id="100402" level="12">
    <decoded_as>json</decoded_as>
    <field name="win.system.eventID">1</field>
    <match>chrome.exe --type=renderer</match>
    <description>CVE-2026-79263: Chrome renderer process spawned with extension context - potential exploitation</description>
    <mitre>
      <id>T1203</id>
    </mitre>
    <group>attack.execution,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 2/4 (CLAIMED) — the patch is claimed by a single source (NVD) and is not independently confirmed via a vendor advisory. Treat the fix as likely but not verified.

1. Immediate Mitigations (while patch verification is pending):

   • Update Chrome to version 152.0.7977.65 or later on all endpoints immediately. This is the only confirmed remediation step.
   • If patching is not immediately possible, restrict extension installation via enterprise policy — allow only approved, vetted extensions and disable all others.
   • Disable automatic extension updates and subscription to untrusted extension sources to reduce the attack surface.
   • Block inbound network traffic to Chrome from untrusted networks (especially internal browsers accessing untrusted internet) pending patch rollout.
   • Enable Chrome's built-in site isolation for all sites (via enterprise policy) to increase the difficulty of exploiting renderer-level flaws.

2. Patch / Upgrade Steps:

   • Deploy Chrome 152.0.7977.65 via the enterprise update channel (Google Update, MSI/WIP for Windows, pkg for macOS, package manager for Linux).
   • Verify rollback protection: set the target version in the enterprise policy to prevent downgrades.
   • After deployment, verify version on all endpoints via endpoint management tools.

3. Long-Term Hardening:

   • Develop and enforce an extension allowlist — extensions are the attack surface for this CVE; minimize their presence in the enterprise.
   • Monitor EPSS and CISA KEV for this CVE. The current EPSS (0.00286) is low, but a public PoC raises the risk of future inclusion in KEV. Re-assess urgency if the CVE enters CISA KEV.
   • Incorporate browser version checks into vulnerability management — treat Chrome as a Tier 1 application with a patching SLA of 48–72 hours for High-severity CVEs.
   • Enable enterprise-wide sandboxing and containerization of browser sessions (e.g., Chrome in a VM/remote browser isolation) to limit the blast radius of sandbox escape chains.
   • Hunt for indicators of prior exploitation — the public PoC suggests the technique may be circulated; review network logs for anomalous extension-related requests and endpoint logs for unusual Chrome process events.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-79263 — Official CVE record with description, CVSS score, and provided metadata. Note: patch status is linked from this source (confidence 2/4).
2. Chromium Security Severity: Referenced within the NVD description — severity classed as Low by the Chromium project; note that NVD's CVSS (8.1) differs from Chromium's internal rating due to differing scoring methodologies.
3. CISA Known Exploited Vulnerabilities (KEV): https://www.cisa.gov/known-exploited-vulnerabilities-catalog — CVE-2026-79263 is NOT listed in KEV as of the report date. Monitor for updates.
4. EPSS (Exploit Prediction Scoring System): https://www.first.org/epss/ — EPSS score of 0.00286 (20.7% percentile), indicating low current exploit likelihood.
5. GitHub / Exploit-DB (PoC): Search for "CVE-2026-79263 PoC" — a public PoC exists per the CVE data; however, as of this report, no verified public exploit code repository or detailed technical write-up is confirmed from the data provided.

Threat Actor Campaigns: No specific threat actor campaigns are publicly attributed to CVE-2026-79263. The public PoC status indicates proof-of-concept availability, but no in-the-wild exploitation or CISA KEV listing has been reported.