Memory Corruption Vulnerability in Cloudflare zlib Library

zlib Updated 02 Oct 2025

Summary

04/01/2024

Disclosed on

N/A

Severity

Yes i

Fix available

Medium

Severity

5.5

CVSS Score

CVE-2023-6992: Cloudflare version of zlib library was found to be vulnerable to memory corruption issues affecting the deflation algorithm implementation (deflate.c). Affects zlib versions < 0. No fix is published. How to fix ↓

Free scan

Check if this vulnerability affects your application

Upload a manifest or SBOM and we'll show whether you're affected, plus every other risky package in the same scan.

Check my app free

No signup required · Results in about 60 seconds

Upload your dependency manifest or SBOM

Drag & drop your file here or Browse

Java Javascript PHP Python Go Rust Ruby Dart C/C++ Elixir CycloneDX SPDX

Upload a supported dependency manifest or SBOM. No installation or source-code access required.

See supported files and SBOM formats

SBOM sbom.json · bom.json · bom.xml · *.spdx.json · *.cdx.json · *.cdx.xml

Java pom.xml · gradle.lockfile · buildscript-gradle.lockfile

Javascript package-lock.json · yarn.lock · pnpm-lock.yaml

PHP composer.lock

Python poetry.lock · requirements.txt · Pipfile.lock

Go go.mod

Rust Cargo.lock

Ruby Gemfile.lock

Dart pubspec.lock

C/C++ conan.lock

Elixir mix.lock

Enter your work email to receive your report link.

Verify your email to view the full report and start 30 days of continuous monitoring. No credit card required.

Background

The Cloudflare version of the zlib library is a widely used open-source compression library that provides functions for data compression and decompression. It is commonly used in various software applications and operating systems. However, a vulnerability has been discovered in the zlib library that affects its deflation algorithm implementation (deflate.c). This vulnerability is caused by improper input validation and a heap-based buffer overflow.

Vulnerability Detail

The memory corruption vulnerability in the Cloudflare zlib library allows a local attacker to exploit the issue during compression using a crafted malicious file. This can potentially lead to a denial of service (DoS) attack on the software. By carefully manipulating the input, an attacker can trigger the buffer overflow and cause the software to crash or become unresponsive. This vulnerability has been assigned the CVE identifier CVE-2023-6992 and has a CVSSv3 score of 5.5, indicating a moderate severity level.

How To Fix

To fix this vulnerability, it is recommended to update the Cloudflare zlib library to the patched version. The issue has been addressed in commit 8352d10 of the zlib repository on GitHub. You can find the patch at the following URL: https://github.com/cloudflare/zlib/commit/8352d108c05db1bdc5ac3bdf834dad641694c13c. By updating to the patched version, the vulnerability will be mitigated.

Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →

Workaround

There is no specific workaround provided for this vulnerability. The recommended approach is to apply the patch mentioned in the 'how_to_fix' section.

Conclusion

The Cloudflare zlib library is vulnerable to a memory corruption issue that can be exploited by a local attacker to cause a denial of service. It is crucial to update to the patched version of the library to mitigate the risk. For further assistance or support in vulnerability remediation, please contact DevNack.com.

See every vulnerability recorded for zlib →