CVE-2021-30632
Google Chromium V8 Out-of-Bounds Write Vulnerability
Description
CVE-2021-30632 is a HIGH out-of-bounds write vulnerability in Google Chromium's V8 JavaScript engine, carrying a CVSS 3.1 score of 8.8. The vulnerability allows a remote attacker to potentially exploit heap corruption via a crafted HTML page. This flaw affects multiple web browsers that utilize Chromium, including Google Chrome, Microsoft Edge, and Opera. Affected products include Google Chrome (< 93.0.4577.82) and Fedora (33; 35). This CVE is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog with a remediation deadline of 2021-11-17. With an EPSS score of 0.83950 (99.29th percentile), this vulnerability demonstrates extremely high real-world exploitation activity and should be prioritized for immediate remediation.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| chrome | < 93.0.4577.82 | |
| fedoraproject | fedora | 33; 35 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
References
- http://packetstormsecurity.com/files/172845/Chrome-JIT-Compiler-Type-Confusion.html(Third Party Advisory, VDB Entry)
- https://chromereleases.googleblog.com/2021/09/stable-channel-update-for-desktop.html(Release Notes)
- https://crbug.com/1247763(Permissions Required)
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4DDW7HAHTS3SDVXBQUY4SURELO5D4X7R/(Release Notes)
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PM7MOYYHJSWLIFZ4TPJTD7MSA3HSSLV2/(Release Notes)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-30632(US Government Resource)
Weakness Type
CWE-787: Out-of-Bounds Write
CVE-2021-30632 is classified under CWE-787 — Out-of-Bounds Write. This weakness occurs when software writes data past the end, or before the beginning, of the intended buffer. Out-of-bounds write vulnerabilities can result in corruption of data, crashes, or execution of arbitrary code. In the context of memory-unsafe languages like C and C++, these vulnerabilities are particularly dangerous because they can overwrite adjacent memory structures, including function pointers, vtables, and heap metadata.
In the context of Google Chromium's V8 engine, this weakness is particularly concerning because V8's JIT compiler generates optimized machine code that performs direct memory operations. When the compiler produces code with incorrect bounds calculations, writes can extend beyond allocated buffer boundaries. In V8, this often occurs through type confusion in the JIT compiler, where incorrect type assumptions lead to miscalculated object sizes or array indices, enabling heap corruption that can be leveraged for arbitrary code execution.
Learn more: CWE-787 — Out-of-Bounds Write
Impact Analysis
CVE-2021-30632 carries a CVSS 3.1 score of 8.8 (HIGH) with Unchanged Scope.
Confidentiality (HIGH): Successful exploitation grants the attacker extensive access to sensitive data within the browser process, including page content, session data, cookies, and potentially saved credentials accessible to the renderer.
Integrity (HIGH): Attackers can corrupt heap memory to inject malicious code, modify browser state, or manipulate web content. The out-of-bounds write primitive enables reliable control over browser process memory.
Availability (HIGH): Complete disruption of the browser process is possible through heap corruption, causing crashes or persistent instability of the affected browser instance.
Scope Unchanged: The vulnerability's scope is Unchanged (U), meaning exploitation is contained within the V8 renderer process. However, when chained with sandbox escape vulnerabilities, full system compromise becomes possible.
With an EPSS score of 0.83950 (99.29th percentile), this vulnerability ranks among the most actively exploited vulnerabilities tracked globally.
Exploit Maturity
CVE-2021-30632 has confirmed active exploitation in the wild and is listed in CISA's Known Exploited Vulnerabilities catalog.
Exploit status: This vulnerability was exploited as a zero-day in the wild before patches were available. Google confirmed active exploitation in the September 2021 stable channel update advisory. Public exploit code demonstrating Chrome JIT compiler type confusion techniques is available on Packet Storm Security. The EPSS score of 0.83950 (99.29th percentile) confirms extremely high exploitation activity.
Ransomware association: As of the latest KEV data, no direct ransomware association has been confirmed for CVE-2021-30632. However, the availability of public exploit code and confirmed zero-day exploitation indicate significant threat actor interest.
Attack surface: Public exploit code exists demonstrating JIT compiler exploitation in Chrome. The vulnerability was patched alongside CVE-2021-30633 in an emergency update, suggesting coordinated zero-day exploitation. Organizations should assume that sophisticated attackers have refined and weaponized this vulnerability.
KEV deadline: CISA required federal agencies to remediate this vulnerability by 2021-11-17. All organizations should treat this deadline as a strong recommendation for their own remediation timelines.
Remediation
- Apply vendor patches immediately. Update Google Chrome to version 93.0.4577.82 or later. Consult the vendor advisory at chromereleases.googleblog.com for specific patch guidance.
- Verify affected product versions in your environment. Identify all instances of Chromium-based browsers in your infrastructure, including Google Chrome (< 93.0.4577.82) and any other Chromium-based browsers. Use asset inventory and vulnerability scanning tools.
- Update all Chromium-based browsers. Since this vulnerability affects the V8 engine in Chromium, ensure all browsers and applications embedding V8 are updated to versions containing the fix.
- Implement interim mitigations if patching is delayed. If immediate patching is not feasible, consider restricting access to untrusted websites, disabling JavaScript for high-risk browsing, and implementing enhanced browser isolation.
- Scan for signs of prior exploitation. Given the confirmed zero-day exploitation, review security logs for evidence of browser-based attacks, suspicious process behavior, or memory corruption indicators.
- Update detection signatures and monitoring rules. Ensure endpoint detection tools and web security gateways are updated to detect exploitation attempts targeting V8 out-of-bounds write vulnerabilities.
Technical Details
CVE-2021-30632 is a HIGH-severity vulnerability in Google Chromium's V8 JavaScript engine that can be exploited remotely over the network. The attack complexity is low, meaning no specialized conditions or preparation are required. No prior authentication or privileges are needed. User interaction is required, meaning a victim must visit a malicious web page containing crafted JavaScript.
Technical mechanism: The vulnerability is an out-of-bounds write in V8's JIT-compiled code. The V8 engine's optimization pipeline can generate machine code that writes beyond allocated buffer boundaries when processing specifically crafted JavaScript. This typically occurs when the compiler's type feedback system is manipulated to produce incorrect assumptions about object layouts, causing the generated code to calculate incorrect write offsets. The resulting heap corruption can be exploited to overwrite adjacent objects, enabling an attacker to construct arbitrary read/write primitives.
Affected products: Google Chrome (< 93.0.4577.82), Fedoraproject Fedora (33; 35)
CVSS 3.1 vector analysis: The vector CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H reflects a network-based attack with low complexity, no privileges required, user interaction required, unchanged scope, and maximum impact across all three CIA dimensions.
Frequently Asked Questions
Is CVE-2021-30632 being actively exploited?
Yes, CVE-2021-30632 was exploited as a zero-day vulnerability in the wild before patches were available. Google confirmed active exploitation in their September 2021 security advisory. Public exploit code exists demonstrating JIT compiler exploitation. The EPSS score of 0.83950 (99.29th percentile) confirms extremely high exploitation probability.
Which products are affected by CVE-2021-30632?
The primary affected product is Google Chrome versions prior to 93.0.4577.82. Since the vulnerability is in the V8 JavaScript engine, other Chromium-based browsers including Microsoft Edge and Opera are likely affected. Fedora Linux distributions (33, 35) with Chromium packages are also impacted.
How do I fix CVE-2021-30632?
Update Google Chrome to version 93.0.4577.82 or later. For other Chromium-based browsers, apply the corresponding vendor updates that include the V8 fix. For Linux distributions, install the latest Chromium security updates from your distribution's package repositories. Verify all instances are patched using vulnerability scanning.
How severe is CVE-2021-30632?
CVE-2021-30632 is rated HIGH with a CVSS 3.1 score of 8.8. Its EPSS score of 0.83950 places it in the 99.29th percentile for exploitation likelihood. The vulnerability was exploited as a zero-day and public exploit code is available. The CISA remediation deadline was 2021-11-17.
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