CVE-2026-111497 in Brotli
Summary
by MITRE • 10/22/2026
A buffer overflow vulnerability in the Brotli decoder (c/dec/decode.c) in Google Brotli versions 1.0.3 through 1.2.0 on all platforms allows a remote unauthenticated attacker to corrupt adjacent decoder state memory, disclose sensitive memory contents, cause a denial of service, or potentially execute arbitrary code using a crafted Brotli-compressed stream.
Users need to update any Brotli libraries or binaries between 1.0.3 through 1.2.0 to the latest available version: 1.0.10 or 1.1.1 or 1.2.1.
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Analysis
by VulDB Data Team • 10/22/2026
The vulnerability identified in Google's Brotli compression library, specifically within versions ranging from 1.0.3 through 1.2.0 across all supported platforms, represents a critical security flaw located in the core decoding logic found in the c/dec/decode.c source file. This buffer overflow condition arises due to insufficient validation of input data boundaries during the decompression process. When an attacker supplies a specially crafted Brotli-compressed stream that exceeds expected memory allocation limits or manipulates internal state variables incorrectly, the decoder fails to properly check array indices and buffer sizes before writing decoded data. This lack of rigorous bounds checking allows for out-of-bounds writes, which directly compromises the integrity of adjacent memory regions used by the decoder's internal state machine. The flaw is particularly dangerous because it can be triggered remotely without any form of authentication, making systems that process user-supplied compressed content highly susceptible to exploitation.
From a technical perspective, this vulnerability aligns with CWE-120, which classifies buffer copy without checking size limits, and more specifically CWE-787, indicating out-of-bounds write vulnerabilities. The operational impact is severe as the corruption of adjacent decoder state memory can lead to multiple adverse outcomes depending on the specific exploitation technique employed by an attacker. In many scenarios, this flaw enables information disclosure where sensitive data residing in nearby memory locations can be read and exfiltrated, potentially leaking cryptographic keys or other confidential application states. Furthermore, the instability introduced by corrupting internal state variables frequently results in crashes that cause denial of service conditions for services relying on Brotli decompression. In more sophisticated attacks, an attacker may leverage this memory corruption to achieve arbitrary code execution with the privileges of the affected process, effectively gaining full control over the compromised system or application environment.
The attack vector associated with this vulnerability is categorized under MITRE ATT&CK techniques related to input validation failures and potentially remote code execution via buffer overflow mechanisms such as T1059 if used for initial access or lateral movement within a networked environment. Systems that accept Brotli-compressed payloads from untrusted sources, including web servers handling compressed HTTP responses or requests, email gateways processing attachments, and any application integrating the vulnerable library versions, are at significant risk. The ability to corrupt memory state means that even if immediate code execution is not achieved, the resulting instability can be used for reliable denial of service attacks against critical infrastructure services.
To mitigate this vulnerability, organizations must immediately audit their software supply chains to identify all instances where Google Brotli libraries between versions 1.0.3 and 1.2.0 are deployed in production or staging environments. The recommended remediation strategy is to upgrade the library to a patched version that includes fixes for these boundary checks. Specifically, users should update to any of the following safe releases: version 1.0.10, version 1.1.1, or version 1.2.1. These versions contain the necessary code changes in the decode.c module to enforce strict bounds checking and prevent out-of-bounds writes during decompression operations. Additionally, implementing defense-in-depth measures such as input validation at application boundaries, deploying web application firewalls that can detect anomalous compressed payloads, and ensuring runtime memory protection mechanisms like ASLR are enabled can further reduce the likelihood of successful exploitation while patching efforts are completed.