CVE-2020-15999: Google Chrome FreeType Heap Buffer Overflow Vulnerability

CVE-2020-15999 is a heap buffer overflow in FreeType, the open-source font rendering library used by Google Chrome. The flaw sits in the function Load_SBit_Png when FreeType processes PNG images embedded inside fonts. Because Chrome relies on FreeType for font handling, a crafted font can trigger the overflow inside the browser process. CISA notes that this vulnerability has been used as part of an exploit chain together with CVE-2020-17087 on Windows and CVE-2020-16010 on Android, which raises the stakes for any organization still running unpatched Chrome instances.

IT and security teams should treat this as a high-priority browser vulnerability: successful exploitation can lead to memory corruption and potential code execution in the context of the browser. Confirm exact affected builds and fixed releases against the vendor advisory before declaring systems clean.

How it works

The weakness is classified as CWE-787 (Out-of-bounds Write). FreeType’s Load_SBit_Png routine fails to enforce proper bounds when it decodes PNG bitmaps that are embedded in font files. An attacker who can supply a malicious font—commonly via a web page that Chrome renders—can cause FreeType to write past the end of a heap buffer. The resulting memory corruption can be leveraged to alter control flow inside the Chrome process.

Public detail does not include exploit code or precise trigger conditions beyond the PNG-in-font path. What is known is that the issue was chained with separate kernel or Android vulnerabilities (CVE-2020-17087 and CVE-2020-16010) to achieve broader impact on those platforms. Defenders should assume that any unpatched Chrome installation that processes untrusted fonts is exposed to this class of attack.

Am I affected? How to find it in your systems

Google Chrome is the primary consumer of the vulnerable FreeType code path. The browser is commonly installed on endpoints, VDI images, kiosks, and developer workstations. Inventory steps:

• Query software inventory or endpoint-management tools for Google Chrome installations and record the exact version string.
• On managed Windows, macOS, and Linux fleets, use package or registry queries to list Chrome versions; compare them with the fixed versions published in the vendor advisory.
• Check whether Chrome is configured to run with additional font-related flags or enterprise policies that might alter FreeType behavior; default configurations are still in scope.
• Review web-proxy, DNS, or EDR telemetry for unusual font downloads or Chrome crashes that coincide with visits to untrusted sites—these can be weak indicators of attempted exploitation, though they are not definitive.

Because the vulnerability lives inside FreeType as shipped with Chrome, other applications that bundle their own FreeType are outside the scope of this specific CVE unless the vendor advisory states otherwise. Always confirm against Google’s security bulletin.

How to remediate

The primary remediation is to apply the Chrome update that addresses CVE-2020-15999, following the vendor’s instructions. CISA’s required action is simply “Apply updates per vendor instructions.”

• Push the patched Chrome release through your standard software-deployment channel as soon as it is validated in a pilot group.
• Verify post-update version numbers on a sample of endpoints to ensure the fix is present.
• For enterprise-managed browsers, enforce automatic updates or a short maximum-version lag so future FreeType issues are closed quickly.
• After patching, restart Chrome processes so the new FreeType library is loaded; a simple version check is insufficient if old processes remain running.

No additional configuration change inside Chrome is documented as a complete substitute for the patch. Harden general browser posture (site isolation, limited extension allow-lists, and least-privilege user accounts) as defense-in-depth for this and similar memory-corruption classes.

If you can't patch immediately

When immediate patching is blocked by change windows or compatibility testing, reduce exposure with compensating controls:

• Segment high-risk user populations (finance, executives, remote workers) onto networks that restrict outbound web access to known-good categories, limiting the chance of receiving a malicious font.
• Deploy virtual-patching rules on web proxies or next-generation firewalls that inspect or block suspicious font MIME types and known exploit kit patterns; treat these as temporary until the Chrome update is installed.
• Disable or restrict Chrome’s ability to load fonts from untrusted origins if an enterprise policy exists for that purpose; confirm the exact policy name and effect in Google’s documentation.
• Increase EDR and browser-crash monitoring for heap-corruption or sandbox-escape telemetry, and alert on any Chrome process that spawns unexpected child processes.
• Where feasible, temporarily shift users to a different hardened browser that does not share the same FreeType build, understanding this is only a stop-gap.

These measures lower likelihood and impact but do not eliminate the vulnerability; schedule the official Chrome update as the definitive fix.

If your data may have been exposed

Actively exploited browser vulnerabilities are frequently used as initial access for broader compromises. Although ransomware use of CVE-2020-15999 is not documented, any successful exploit chain could lead to credential theft, session hijacking, or further lateral movement. If you suspect exposure, preserve relevant Chrome crash dumps and EDR timelines, reset credentials for affected users, and review access logs for anomalous activity. You can also run a free exposure scan of your email addresses against known breach data sets to determine whether associated accounts have appeared in prior incidents.