CVE-2021-39293 Overview
CVE-2021-39293 is a Denial of Service vulnerability in the Go programming language's archive/zip package. A crafted archive header that falsely designates many files as present can cause a NewReader or OpenReader panic, resulting in application crashes. This vulnerability exists because of an incomplete fix for the previously addressed CVE-2021-33196.
Critical Impact
Applications using Go's archive/zip package to process untrusted ZIP files can be crashed by maliciously crafted archives, causing service disruption.
Affected Products
- Golang Go versions before 1.16.8
- Golang Go versions 1.17.x before 1.17.1
- NetApp Cloud Insights Telegraf
Discovery Timeline
- 2022-01-24 - CVE-2021-39293 published to NVD
- 2024-11-21 - Last updated in NVD database
Technical Details for CVE-2021-39293
Vulnerability Analysis
This vulnerability falls under CWE-770 (Allocation of Resources Without Limits or Throttling). The archive/zip package in Go fails to properly validate archive headers when processing ZIP files. An attacker can create a malicious ZIP file with a header that claims to contain an extremely large number of files. When the NewReader or OpenReader functions attempt to process this crafted archive, they trigger a panic condition instead of gracefully handling the invalid input.
The vulnerability is particularly concerning because it represents an incomplete fix for CVE-2021-33196, indicating that the original patch did not fully address all attack vectors related to malicious archive header manipulation. This enables network-based attackers to cause denial of service conditions without requiring any authentication or user interaction.
Root Cause
The root cause is improper resource allocation handling in the ZIP archive parsing logic. When the archive/zip package reads a ZIP file header, it allocates resources based on the declared number of files in the archive without adequate validation. A maliciously crafted header can specify an unreasonably large file count, leading to uncontrolled resource allocation that triggers a panic condition in the Go runtime.
Attack Vector
An attacker can exploit this vulnerability by providing a specially crafted ZIP file to any application using vulnerable versions of Go's archive/zip package. The attack requires no authentication and can be executed remotely over the network. Common attack scenarios include:
- Uploading malicious ZIP files to web applications that process user-uploaded archives
- Sending crafted archives to services that automatically extract or inspect ZIP files
- Targeting automated build systems or CI/CD pipelines that process external archives
The vulnerability does not require user interaction beyond the application processing the malicious file. For detailed technical information, see the Golang Announcement.
Detection Methods for CVE-2021-39293
Indicators of Compromise
- Application crashes or panics when processing ZIP files
- Unexpected service restarts in Go-based applications handling archive files
- Log entries indicating panic conditions in archive/zip package functions
- Error messages referencing NewReader or OpenReader panic states
Detection Strategies
- Monitor application logs for Go runtime panic messages related to archive/zip operations
- Implement file validation checks before passing archives to vulnerable functions
- Deploy intrusion detection rules to identify abnormally structured ZIP file headers
- Track application stability metrics for services that process user-supplied archives
Monitoring Recommendations
- Enable verbose logging for archive processing operations in Go applications
- Monitor system resources for unusual memory allocation patterns during ZIP processing
- Set up alerts for application crash patterns indicative of DoS attacks
- Review uploaded files for suspicious archive header characteristics
How to Mitigate CVE-2021-39293
Immediate Actions Required
- Upgrade Go to version 1.16.8 or later for the 1.16.x branch
- Upgrade Go to version 1.17.1 or later for the 1.17.x branch
- Recompile all Go applications using vulnerable versions of the standard library
- Implement input validation for ZIP files before processing
Patch Information
The vulnerability is fixed in Go versions 1.16.8 and 1.17.1. Organizations should update their Go installations and rebuild affected applications. For additional guidance, review the following resources:
Workarounds
- Implement pre-processing validation of ZIP files to check header integrity before passing to archive/zip functions
- Deploy application-level rate limiting and size restrictions for archive uploads
- Use containerization to isolate archive processing and limit impact of panic conditions
- Consider implementing recovery mechanisms using Go's recover() function around archive processing code
# Verify Go version to ensure patched version is installed
go version
# Expected output should show 1.16.8+, 1.17.1+, or newer
# Rebuild affected applications after Go upgrade
go build -a ./...
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
