External risk intelligence

MiniZip Heap Overflow Vulnerability in zlib and pyminizip.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2023-45853

The vulnerability resides in a compression library (MiniZip/zlib) used as a developer dependency or utility within applications. It is not an internet-facing service, appliance, or edge gateway. The code is typically executed locally or within backend processes that handle files, making public internet exposure as a direct reachable attack surface very unlikely.

Integer Overflow

Zlib

before 1.3.10.2.6 and earlier

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability in zlib's MiniZip component could allow attackers to disrupt systems by exploiting an integer overflow flaw related to file handling. While not a direct internet-facing issue, this vulnerability exists in a widely used compression library, potentially impacting various applications if they utilize the affected code. The main concern is confirming relevance and exposure within our environment.

A library flaw can crash systems via file operations.
It affects software that handles compressed files.
Confirm if our systems use this specific library.

Attack Path

How an attacker could exploit the issue

An attacker could reach this vulnerability by sending a specially crafted zip file to an application that uses the affected compression library. This could occur over a network if the application processes remote files, or through a local file upload. The vulnerability exists within the MiniZip component, which handles the creation of new files within a zip archive. Exploiting this could lead to significant system compromise.

No authentication or special access needed.
Triggered by processing a long filename.
Leads to application crash or code execution.

Live Threat

Current exploitation, exposure, and threat context

When processing specially crafted zip files, an integer overflow and heap-based buffer overflow could occur. This might affect the integrity and availability of services handling these files when using affected versions of the MiniZip library or applications that bundle it.

System integrity and availability.
Processing maliciously crafted zip files.
Denial of service or data corruption.

Operational Fix

Recommended remediation, mitigation, and detection steps

The zlib library's MiniZip component is affected by a vulnerability that could be triggered by crafted filenames, comments, or extra fields during ZIP file creation. While MiniZip is not a supported part of zlib, it is bundled with pyminizip, making that library also vulnerable. Application owners and platform teams should prioritize identifying where zlib or pyminizip are utilized, assessing potential exposure through file handling processes, and planning remediation based on risk.

Application owners and platform teams responsible.
Verify zlib/pyminizip usage and file processing exposure.
Plan remediation during maintenance windows.

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 zlib and the MiniZip component?

zlib is a fundamental, widely used software library that provides data compression services. MiniZip is a specific utility included within the zlib source distribution that developers use to handle and create ZIP archive files. While zlib itself is a robust and maintained product, MiniZip is provided as a sample or contribution, meaning it does not receive the same level of official maintenance or support as the core zlib compression library.

What does CVE-2023-45853 mean for system security?

This vulnerability is classified as an integer overflow, which leads to a heap-based buffer overflow. In plain terms, the software fails to properly calculate the space required when processing excessively long filenames or metadata in a ZIP file. This memory error can allow an attacker to overwrite adjacent data in the computer's memory, potentially leading to a system crash or allowing unauthorized code execution.

How is this zlib vulnerability triggered?

The flaw is triggered when an application uses the affected MiniZip code to process a maliciously crafted ZIP file containing an unusually long filename, comment, or extra field. The vulnerability does not trigger if the application is simply storing or moving standard, well-formed ZIP archives. It specifically requires the library to attempt to parse or create entries within the archive that exceed the expected size limits.

Why is this vulnerability considered low-risk by Halo Surface Signal?

Halo Surface Signal notes that this vulnerability is very unlikely to be reachable from the public internet. Because the flawed code is embedded within backend libraries that handle file processing, it is not an internet-facing service or appliance itself. An attacker would typically need to find an application that accepts and processes external files, making a direct, remote attack on a standard edge gateway or service quite difficult.

What should I do if I use zlib or pyminizip?

First, conduct an inventory to determine if your software uses zlib or the pyminizip package. Focus your search on backend services or tools that handle file uploads or archive creation. If you find these components, check your software's documentation or package managers for updates to patched versions. Consult your development or platform teams to plan a transition to secure versions during your next maintenance cycle.

References

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.