CVE-2021-37975 Overview
CVE-2021-37975 is a use-after-free vulnerability in the V8 JavaScript engine used by Google Chrome versions prior to 94.0.4606.71. A remote attacker can exploit heap corruption by serving a crafted HTML page to a victim browser, potentially leading to arbitrary code execution within the renderer process. The flaw is tracked under CWE-416 and was added to the CISA Known Exploited Vulnerabilities catalog, confirming in-the-wild exploitation. The vulnerability affects Google Chrome, Fedora, and Debian distributions that ship the vulnerable Chromium codebase.
Critical Impact
Successful exploitation enables remote heap corruption in V8, allowing attackers to execute arbitrary code in the browser context after a user visits a malicious page.
Affected Products
- Google Chrome prior to 94.0.4606.71
- Fedora 33, 34, and 35
- Debian Linux 10 and 11
Discovery Timeline
- 2021-10-08 - CVE-2021-37975 published to NVD
- 2025-10-24 - Last updated in NVD database
- CISA KEV - Listed as a Known Exploited Vulnerability by CISA
Technical Details for CVE-2021-37975
Vulnerability Analysis
The vulnerability resides in V8, the JavaScript and WebAssembly engine that powers Chromium-based browsers. A use-after-free condition occurs when V8 retains a reference to a heap object after that object has been freed. Subsequent operations on the dangling reference allow an attacker to corrupt the V8 heap.
Because V8 manages JavaScript objects with complex lifecycle and garbage collection semantics, an attacker who can influence object allocation and freeing through scripted page content can groom the heap. Crafted JavaScript on a malicious HTML page triggers the freed-object reuse path and steers execution toward attacker-controlled data.
Root Cause
The root cause is improper object lifetime management inside V8 [CWE-416]. When an internal handle or pointer references an object that has already been released, V8 reuses memory that the attacker can repopulate with controlled values. Treating the freed memory as a valid object leads to type confusion or pointer corruption inside the engine.
Attack Vector
Exploitation requires a victim to load attacker-controlled HTML and JavaScript in a vulnerable Chrome build. Delivery mechanisms include phishing links, malvertising, watering-hole sites, and compromised legitimate domains. No authentication is required, and only user interaction in the form of page navigation is needed. Refer to the Packet Storm report and Chromium bug 1252918 for engine-level details.
No verified public proof-of-concept code is reproduced here. The vulnerability is described in prose; consult the upstream advisories for technical specifics.
Detection Methods for CVE-2021-37975
Indicators of Compromise
- Chrome renderer processes crashing with heap corruption signatures shortly after visiting an untrusted page.
- Spawning of unexpected child processes from chrome.exe or the Chromium renderer, especially shell or scripting hosts.
- Outbound connections to newly registered or low-reputation domains immediately following browser activity.
- Browser binaries running at vulnerable versions below 94.0.4606.71 on managed endpoints.
Detection Strategies
- Inventory installed Chrome and Chromium-derived browser versions and flag any build older than 94.0.4606.71.
- Correlate browser process crashes with subsequent process creation, file write, or network events to identify post-exploitation behavior.
- Hunt for renderer-spawned LOLBins such as powershell.exe, cmd.exe, wscript.exe, or rundll32.exe.
- Monitor for anomalous in-memory code patterns originating from V8 sandboxed renderer processes.
Monitoring Recommendations
- Forward endpoint browser telemetry, including process lineage and module loads, into a SIEM for retrospective hunting.
- Track navigation logs from web proxies and DNS resolvers for traffic to known exploit-hosting infrastructure tied to CISA KEV reporting.
- Alert on Chrome auto-update failures so out-of-date browsers do not silently persist in the environment.
How to Mitigate CVE-2021-37975
Immediate Actions Required
- Update Google Chrome to version 94.0.4606.71 or later on all managed endpoints.
- Patch downstream Chromium-based distributions using Debian Security Advisory DSA-5046 and the corresponding Fedora package announcements.
- Restart browser sessions after patch deployment to ensure the vulnerable V8 module is unloaded.
- Verify compliance against the CISA KEV listing given confirmed in-the-wild exploitation.
Patch Information
Google fixed the vulnerability in the stable channel release announced in the Chrome Releases blog. The fix shipped in Chrome 94.0.4606.71. Debian addressed the issue in the chromium package via DSA-5046, and Fedora published updated chromium builds for Fedora 33, 34, and 35.
Workarounds
- Enforce Chrome auto-update through enterprise policy to prevent version drift.
- Restrict browsing to trusted domains via web proxy categorization for hosts that cannot be patched immediately.
- Disable JavaScript on high-risk endpoints until patching completes, accepting reduced functionality.
- Isolate browsing activity in remote browser isolation or virtualized environments for sensitive users.
# Verify Chrome version on Linux endpoints
google-chrome --version
# Update Chromium on Debian/Ubuntu
sudo apt-get update && sudo apt-get install --only-upgrade chromium
# Update Chromium on Fedora
sudo dnf upgrade --refresh chromium
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
