External risk intelligence

Google Brotli Decoder Buffer Overflow Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.2)

CVE-2026-111497

Brotli is a widely used compression algorithm integrated into many web servers, browsers, and network applications to process internet traffic. Because it is commonly used to handle external data streams in public-facing web services, APIs, and browsers, it frequently processes untrusted input directly from the internet, making it a likely component of an internet-facing attack surface.

Out-of-bounds Write

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical vulnerability has been identified in the Brotli decompression technology, which is used to compress and decompress data across various applications, including web services and browsers. This issue could allow an attacker to disrupt services or potentially access sensitive information through specially crafted data streams. The main concern is confirming whether our environment utilizes the affected versions of this technology.

Compromised data compression technology.
Potential for service disruption or data exposure.
Confirm use of affected compression tools.

Attack Path

How an attacker could exploit the issue

An attacker can exploit this vulnerability by sending a specially crafted Brotli-compressed stream over the network to a system using a vulnerable Brotli decoder. This crafted stream can cause a buffer overflow, leading to memory corruption, data disclosure, denial of service, or even arbitrary code execution.

Network access required.
Crafted Brotli stream triggers overflow.
Potential for code execution and DoS.

Live Threat

Current exploitation, exposure, and threat context

A buffer overflow in the Brotli decoder could allow an attacker to corrupt memory, potentially leading to information disclosure, denial of service, or arbitrary code execution when processing a crafted Brotli-compressed stream.

Decoder memory corruption.
Crafted compressed stream input.
Denial of service or code execution.

Operational Fix

Recommended remediation, mitigation, and detection steps

This critical vulnerability in the Brotli decoder impacts any system processing Brotli-compressed streams, potentially leading to memory corruption, sensitive data disclosure, denial of service, or arbitrary code execution. Ownership will likely fall to application teams if Brotli is an integrated library, or platform/infrastructure teams if it's part of a core service or network appliance. The first practical move is to identify all instances of Brotli versions 1.0.3 through 1.2.0 within your environment, assess their exposure (especially internet-facing services), and confirm the accountable owner before planning remediation.

Identify Brotli library usage and owners.
Verify exposure of affected Brotli instances.
Plan remediation based on identified risks.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is Google Brotli and why is it used?

Brotli is an open-source compression algorithm created by Google. It is widely used to shrink the size of web content, such as HTML, CSS, and JavaScript files, to speed up data transfer. Because it effectively reduces file sizes, it is integrated into many web browsers, servers, and network applications to optimize how information moves across the internet.

What is the buffer overflow weakness in CVE-2026-111497?

A buffer overflow occurs when a program tries to store more data in a temporary storage area, known as a buffer, than it can hold. In this CVE, the Brotli decoder fails to properly manage memory when processing a malicious data stream. This allows extra data to overwrite adjacent memory, which can lead to system crashes, unauthorized access to sensitive information, or the execution of malicious instructions.

How does an attacker trigger this Brotli vulnerability?

An attacker triggers this issue by sending a specially crafted, malicious Brotli-compressed data stream to a vulnerable application or service. The decoder attempts to process this input and suffers a memory error. Simply having the library installed is not enough to trigger the flaw; the software must actively receive and decode external, untrusted compressed data from a network source.

Is my environment at risk from this Brotli flaw?

Halo Surface Signal indicates that because Brotli is frequently used to handle untrusted traffic in public-facing web services, APIs, and browsers, it is a likely component of an internet-facing attack surface. You should prioritize checking services that directly process external data streams, as these are the most accessible paths for an attacker to exploit the vulnerability remotely.

How should I respond to CVE-2026-111497?

Begin by inventorying your applications and infrastructure to locate any instances of the Brotli decoder running versions 1.0.3 through 1.2.0. Once identified, coordinate with the appropriate application or platform teams to update those libraries or binaries to version 1.0.10, 1.1.1, or 1.2.1. Confirming the specific version in use is the most critical first step to ensuring your software is no longer vulnerable to this memory corruption.

References

nodejs.org/en/blog/vulnerability/october-2026-security-releases

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.