CVE-2026-115946 in XS::libbrotli
Summary
by MITRE • 11/01/2026
XS::libbrotli versions before 1.2.1.0 for Perl bundle a brotli library with an out-of-bounds write in the decoder.
Affected versions compile a bundled brotli into static archives that dependent XS modules link against at build time, rather than using the system library. The bundled copy, 1.0.7 or 1.1.0 across the range, carries the decoder out-of-bounds write described in CVE-2026-111497. Version 1.2.1.0 updates it to brotli 1.2.1.
XS::libbrotli has no Perl interface, so the decoder is reached through any dependent module that decompresses untrusted data with it. An attacker supplying a crafted brotli stream can corrupt decoder state, disclose memory, crash the process, or potentially execute arbitrary code. Upgrading the system brotli does not remediate this.
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Analysis
by VulDB Data Team • 11/01/2026
The XS::libbrotli module for Perl presents a significant security risk due to its bundling of an outdated and vulnerable version of the Brotli compression library. Versions prior to 1.2.1.0 incorporate static copies of brotli, specifically versions 1.0.7 or 1.1.0, which are linked directly into dependent XS modules at build time rather than relying on system-installed libraries. This architectural choice isolates the vulnerability from standard system updates, meaning that even if a host operating system is patched against known Brotli flaws, applications using these older Perl module versions remain exposed. The core issue stems from CVE-2026-111497, which identifies an out-of-bounds write flaw within the decoder component of the bundled library. This vulnerability allows for memory corruption when processing malformed input data, creating a pathway for severe exploitation scenarios that compromise both confidentiality and integrity.
From a technical perspective, the out-of-bounds write occurs during the decoding process when the parser encounters crafted Brotli streams designed to trigger invalid memory access patterns. Because XS::libbrotli lacks its own Perl interface, the vulnerability is not directly accessible through standard Perl scripting but is instead exposed indirectly through any dependent module that utilizes this library for decompression tasks. When an attacker supplies a specially constructed compressed stream, they can manipulate internal decoder state variables beyond their allocated boundaries. This memory corruption can lead to arbitrary code execution if the attacker successfully controls the overwritten data structures or causes a denial of service by crashing the application process. The severity is amplified by the fact that many Perl-based web applications and API gateways rely on such modules for handling compressed HTTP payloads, making them prime targets for remote exploitation over network interfaces.
The operational impact of this vulnerability extends beyond simple crashes to include potential data exfiltration and full system compromise. An attacker leveraging this flaw can read sensitive information from adjacent memory regions that were not intended to be accessed, leading to the disclosure of credentials, session tokens, or other confidential application data. Furthermore, by carefully crafting the input stream to control heap layout and overwrite function pointers or object vtables, an adversary may achieve remote code execution with the privileges of the compromised process. This aligns closely with CWE-787, which classifies out-of-bounds writes as a critical memory safety error, and maps to MITRE ATT&CK techniques involving exploitation for initial access or privilege escalation depending on the context in which the vulnerable module is deployed. The inability to remediate this issue by simply updating system-level libraries underscores the importance of managing third-party dependencies within application codebases independently.
Mitigation strategies must focus primarily on upgrading XS::libbrotli to version 1.2.1.0 or later, which integrates a patched version of the Brotli library that resolves the decoder vulnerability. Organizations should audit their Perl dependency trees using tools like cpanm or Carton to identify and update affected modules promptly. In environments where immediate patching is not feasible, implementing strict input validation at the application layer can provide partial protection by rejecting malformed compressed data before it reaches the vulnerable decoder logic. Additionally, deploying runtime security measures such as address space layout randomization and stack canisters can mitigate the likelihood of successful exploitation by making memory corruption attacks more difficult to execute reliably. Regular vulnerability scanning focused on Perl module dependencies is essential to maintain a secure posture against these types of supply chain vulnerabilities.